 Lecture 7. The Pioneers of Science by Oliver Lodge. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information to volunteer, please visit LibriVox.org. Pioneers of Science by Oliver Lodge. Lecture 7. Sir Isaac Newton. Summary of facts for Lecture 7 and 8. Otto Gurek, 1602 to 1686. The Honorable Robert Boyle, 1626 to 1691. Huygens, 1629 to 1695. Christopher Wren, 1632 to 1723. Robert Hook, 1635 to 1702. Newton, 1642 to 1727. Edmund Haley, 1656 to 1742. James Bradley, 1692 to 1762. Chronology of Newton's life. Isaac Newton was born at Woolsthorpe near Grantham Lincolnshire on Christmas Day, 1642. His father, a small freehold farmer, also named Isaac, died before his birth. His mother, Ni, Hannah A. Scowl, in two years married a Mr. Smith, rector of North Witham. But was again left a widow in 1656. His uncle W. A. Scowl was rector of a near parish and a graduate of Trinity College, Cambridge. At the age of 15, Isaac was removed from school at Grantham to be made a farmer of. But, as it seemed, he would not make a good one. His uncle arranged for him to return to school and thence to Cambridge, where he entered Trinity College as a sub-sizer in 1661, studied Descartes' geometry, found out a method of infinite series in 1665, and began the invention of Fluctions. In the same year in the next, he was driven from Cambridge by the plague. In 1666, at Woolsthorpe, the apple fell. In 1667, he was elected a fellow of his college, and in 1669 was specially noted as possessing an unparalleled genius by Dr. Barrow, first occasion professor of mathematics. The same year, Dr. Barrow retired from his chair in favor of Newton, who was thus elected at the age of 26. He lectured first on optics was great success. Early in 1672, he was elected a fellow of the Royal Society and communicated his researches in optics, his reflecting telescope, and his discovery of the compound nature of white light. Annoying controversies arose, but he nevertheless contributed good many other most important papers and optics, including observations in diffraction and colors of thin plates. He also invented the modern sextant. In 1672, a letter from Paris was read at the Royal Society, concerning a new and accurate determination of the size of the earth by Picard. When Newton heard of it, he began the Principia working in silence. In 1684 arose a discussion between Wren, Hook, and Haley concerning the law of inverse square as applied to gravity and the path that would cause the planets to describe. Hook asserted that he had a solution, but he would not produce it. After waiting some time for it, Haley went to Cambridge to consult Newton on the subject, and thus discovered the existence of the first part of the Principia. We are in all this, and much more was thoroughly worked out. On his representations to the Royal Society, the manuscript was asked for that when complete was printed and published in 1687 at Haley's expense. While it was being completed, Newton and seven others were sent to uphold the dignity of the University before the Court of High Commission and Judge Jeffries, against a high-handed action of James II. In 1682 he was sent to Parliament and was present at the coronation of William and Mary, made friends with Locke. In 1692 Montague, Lord Halifax, made him warden, and in 1697 Master of the Mint, Winston succeeded him as Lucasian professor. In 1693 the method of fluxions was published. In 1703 Newton was made president of the Royal Society and held the office to the end of his life. In 1705 he was knighted by Anne. In 1713 Codes helped him to bring out a new edition of the Principia, completed as we now have it. On the 20th of March 1727 he died, having lived from Charles I to George II. The laws of motion discovered by Galileo stated by Newton. Law 1. If no force acts on a body in motion, it continues to move uniformly and straight line. Law 2. If force acts on a body, it produces a change of motion proportional to the force and in the same direction. Law 3. When one body exerts force on another, that other reacts with equal force upon the one. Lecture 7 Sir Isaac Newton The little hamlet of Woolsthorpe lies close to the village of Colsterworth, about six miles south of Grantham, in the county of Lincoln. In the manor house of Woolsthorpe, on Christmas Day 1642, was born to a widowed mother, a sickly infant, who seemed not long for this world. Two women were sent to North Witham to get some medicine for him, scarcely expecting to find him alive on their return. However, the child lived, became fairly robust, and was named Isaac after his father. What sort of man this father was, we do not know. He was what we may call a yeoman, that most wholesome and natural of all classes. He owned the soil he tilled, and his little estate had already been in the family for some hundred years. He was 36 when he died, and had only been married a few months. Of the mother, unfortunately, we know almost as little. We hear that she was recommended by a parishioner to the Reverend Barnabas Smith, an old bachelor in search of a wife, as the widow Newton, an extraordinary good woman, and so I expect she was a thoroughly sensible, practical, homely, industrious, middle-class, mill-on-the-floss sort of woman. However, on her second marriage she went to live at North Witham, and her mother, Old Mrs. Ayskow, came to superintend the farm at Woolsthorpe, and take care of young Isaac. By her second marriage, his mother acquired another piece of land, which she settled on her first son. So Isaac found himself heir to two little properties, bringing in a rental of about 80 pounds a year. He had been sent to a couple of village schools to acquire the ordinary accomplishments taught at those places, and for three years to the grammar school at Grantham, then conducted by an old gentleman named Mr. Stokes. He had not been very industrious at school, nor did he feel keenly the fascinations of the Latin grammar, for he tells us that he was the last boy in the lowest class but one. He used to pay much more attention to the construction of kites and windmills and water-wheels, all of which he made to work very well. He also used to tie paper lanterns to the tail of his kite, so as to make the country folk fancy they saw a comet, and in general to despot himself as a boy should. It so happened, however, that he succeeded in threshing and fair fight a bigger boy who was higher in the school and who had given him a kick. His success awakened a spirit of emulation and other things than boxing, and young Newton speedily rose to be top of the school. Under these circumstances, at the age of fifteen, his mother, who would now return to Wool's thought, which had been rebuilt, thought it was time to train him for the management of his land and to make a farmer and grazier of him. The boy was doubtless glad to get away from school, but he did not take kindly to the farm, especially not to the marketing at Grantham. He and an old servant were sent to Grantham every week to buy and sell produce, but young Isaac used to leave his old mentor to do all the business, and himself retired to an attic in the house he had lodged in when at school, and they are buried himself in books. After a time he didn't even go through the farce of visiting Grantham at all, but stopped on the road and sat under a hedge, reading or making some model until his companion returned. We hear of him now in the great storm of 1658, the storm on the day Cromwell died, measuring the force of the wind by seeing how far he could jump with it and against it. He also made a water-clock and set it up in the house at Grantham, where it kept fairly good time so long as he was in the neighborhood to look after it occasionally. At his home and home he made a couple of sundials on the side of the wall. He began by marking the position of the sun by the shadow of a peg driven into the wall, but this gradually developed in a regular dial, one of which remained for use for some time and was still to be seen in the same place during the first half of the present century, only with the gnome and gone. In 1844 the stone on which it was carved was carefully extracted and presented to the Royal Society, who preserved it in their library. The letters W-T-O-N, roughly carved on it, are barely visible. All these pursuits must have been rather trying to his poor mother, and she probably complained to her brother, the rector of Burton Coggles. At any rate this gentleman found Master Newton one morning under a hedge when he ought to have been farming, but as he found him working away at Mathematics, like a wise man he persuaded his sister to send the boy back to school for a short time, and then to Cambridge. On the day of his finally leaving school, old Mr. Stokes assembled the boys, made them a speech in praise of Newton's character and ability, and then dismissed him to Cambridge. At Trinity College a new world opened out before the country bred lad. He knew his classics passively, but of mathematics and science he was ignorant, except through the smatterings he had picked up for himself. He devoured a book on logic and another on Kepler's optics, so fast that his attendance at lectures on these subjects became unnecessary. He also got hold of Euclid and of Descartes' geometry. The Euclid seemed childishly easy and was thrown aside, but the Descartes baffled him for a time. However, he set to it again and again, and before long mastered it. He threw himself heart and soul into mathematics, and very soon made some remarkable discoveries. First he discovered the binomial theorem, familiar now to all who have done any algebra, unintelligible to others, and therefore I say nothing about it. By the age of 21 or 2 he had begun his great mathematical discovery of infinite series and fluxions, now known by the name of differential calculus. He wrote these things out and must have been quite absorbed in them, but it never seems to have occurred to him to publish them or to tell anyone about them. In 1664 he noticed some halos around the moon, and as his manner was he measured their angles. The small ones three and five degrees each, the larger one 22 degrees 35 minutes later he gave their theory. Small colored halos round the moon are often seen and are said to be a sign of rain. They are produced by the action of minute globules of water or cloud particles upon light, and are brightest when the particles are nearly equal in size. They are not like the rainbow, every part of which is due to light that has entered a raindrop and been refracted and reflected with prismatic separation of colors. A halo is caused by particles so small as to be almost comparable with the size of waves of light, in a way which is explained in optics under the head diffraction. It may be easily imitated by dusting an ordinary piece of window glass over with lycopodium, placing a candle near it and then looking at the candle flame through the dusty glass from a fair distance. Or you may look at the image of a candle in a dusted looking glass. Lycopodium dust is specially suitable for its granules are remarkably equal in size. The large halo, more rarely seen, of angular radius 22 degrees 35 minutes is due to another cause again and is a prismatic effect, although it exhibits hardly any color. The angle 22 and a half degrees is characteristic of refraction in crystals with angles of 60 degrees and refractive index about the same as water. In other words this halo is caused by ice crystals in the higher regions of the atmosphere. He almost the same year observed a comet and sat up so late watching it that he made himself ill. By the end of the year he was elected to a scholarship and took his BA degree. The order of merit for that year never existed or has not been kept. It would have been interesting not as a testimony to Newton but to the sense or nonsense of the examiners. The oldest professorship of mathematics at the University of Cambridge, the Lucasian, had not then been long founded and its first occupant was Dr. Isaac Barrow, an eminent mathematician and a kind old man. With him Newton made good friends and was helpful in preparing a treatise on optics for the press. His help was acknowledged by Dr. Barrow in the preface which states that he had corrected several errors and made some capital additions of his own. Thus we see that although the chief part of his time was devoted to mathematics, his education was already directed to both optics and astronomy. Kepler, Descartes, Galileo all combined some optics with astronomy. Tycho and the old ones combined alchemy. Newton dabbled in this also. Newton reached the age of 23 in 1665, the year of the Great Plague. The plague broke out in Cambridge as well as in London and the whole college was sent down. Newton went back to Wolsthorpe, his mind teaming with ideas, this year and part of the next in quiet pondering. Somehow or other he had got hold of the notion of centrifugal force. It was six years before Hagen's, discovered and published the laws of centrifugal force. But in some quiet way of his own Newton knew about it and applied the idea to the motion of the planets. We can almost follow the course of his thoughts as he brooded and meditated on the great problem which attacks so many previous thinkers. What makes the planets move round the sun? Kepler had discovered how they moved, why did they so move, what urged them? Even the how took a long time. All the time of the Greeks through Ptolemy, the Arabs, Copernicus, Tycho, circular motion, epicycles and eccentrics had been the prevailing theory. Kepler with his marvelous industry had rested from Tycho's observations the secret of their orbits. They moved in ellipses with the sun in one focus. Their rate of description of area, not their speed, was uniform and proportional to time. Yes, in a third law, a mysterious law of unintelligible import had also yielded itself to his penetrating industry. A law, the discovery of which had given him the keenest delight and excited an outburst of rapture, vis that there was a relation between the distances and the periodic times of the several planets. The cubes of the distances were proportional to the squares of the times for the whole system. This law first found true for the six primary planets he had also extended after Galileo's discovery to the four secondary planets or satellites of Jupiter. But all this was working in the dark. It was only the first step. This empirical discovery of facts, the facts were so, but how came they so? What made the planets move in this particular way? Descartes' vortices was an attempt, a poor and imperfect attempt, at an explanation. It had been hailed and adopted throughout Europe for one of a better, but it did not satisfy Newton. No, it proceeded on a wrong tack, and Kepler had proceeded on a wrong tack in imagining spokes or rays sticking out from the sun and driving the planets round like a piece of mechanism or millwork. For note that all these theories are based on a wrong idea. The idea, these, that some force is necessary to maintain a body in motion. But this was contrary to the laws of motion as discovered by Galileo. You know that during his last years of blind helplessness at our century, Galileo had pondered and written much on the laws of motion, foundation of mechanics. In his early youth at Pisa, he had been similarly occupied. He had discovered the pendulum. He had refuted the Aristotelians by dropping weights from the Leaning Tower, which we must rejoice that no earthquake has yet injured. And he had returned to mechanics at intervals all his life. And now, when his eyes were useless for astronomy, when the outer world has become to him only a prison to be broken by death, he returns once more to the laws of motion and produces the most solid and substantial work of his life. For this is Galileo's main glory, not his brilliant exposition of the Copernican system, not his flashes of wit at the expense of a more abundant philosophy, not his experiments on floating bodies, not even his telescope and astronomical discoveries, though these are the most taking and dazzling at first sight. No, his main glory entitled to immortality consists in this, that he first laid the foundation of mechanics on a firm and secure basis of experiment, reasoning, and observation. He first discovered the true laws of motion. I said little of this achievement in my lecture on him, for the work was written towards the end of his life, and I had no time then. But I knew I should have to return to it before we came to Newton, and here we are. You may wonder how the work got published when so many of his manuscripts were destroyed. Horrible to say, Galileo's own son destroyed a great bundle of his father's manuscripts, thinking, no doubt, thereby to save his own soul. This book on mechanics was not burned, however. The fact is it was rescued by one or other of his pupils, Torcelli or Viviani, who were allowed to visit him in his last two or three years. It was kept by them for some time and then published surreptitiously in Holland, not that there is anything in it bearing in any visible way on any theological controversy. But it is unlikely that the Inquisition would have suffered it to pass, not withstanding. I have appended to the summary proceeding this lecture the three axioms or laws of motion discovered by Galileo. They are stated by Newton with an example of clearness and accuracy, and are hence known as Newton's laws, but they are based on Galileo's work. The first is the simplest, though ignorance of it gave the ancients a deal of trouble. It is simply a statement that force is needed to change the motion of a body, i.e., that if no force act on a body it will continue to move uniformly both in speed and direction, in other words, steadily in a straight line. The old idea had been that some force was needed to maintain motion. On the contrary, the first law asserts some force is needed to destroy it, leave a body alone, free from all friction or other retiring forces, and it will go on forever. The planetary motion through empty space therefore wants no keeping up. It is not the motion that demands a force to maintain it. It is the curvature of the path that needs a force to produce it continually. The motion of a planet is approximately uniform so far as speed is concerned, but it is not constant in direction. It is nearly a circle. The real force needed is not a propelling but a deflecting force. The second law asserts that when a force acts the motion changes, either in speed or in direction or both. Add a pace proportional to the magnitude of the force and in the same direction as that in which the force acts. Now, since it is almost solely in direction that planetary motion alters, a deflecting force only is needed. A force at right angles to the direction of motion, a force normal to the path. Considering the motion is circular, a force along the radius, a radial or centripetal force must be acting continually. Whirl a weight round and around by a bit of elastic. The elastic is stretched. Whirl it faster, it is stretched more. The moving mass pulls at the elastic. That is its centrifugal force. The hand at the center pulls also. That is centripetal force. The third law asserts that these two forces are equal and together constitute the tension in the elastic. It is impossible to have one force alone. There must be a pair. You can't push hard against a body that offers no resistance. Whatever force you exert upon a body, with that same force the body must react upon you. Action and reaction are always equal and opposite. Sometimes an absurd difficulty is felt with respect to this. Even by engineers, they say, if the cart pulls against the horse with precisely the same force as the horse pulls the cart, why should the cart move? Why on earth not? The cart moves because the horse pulls it and because nothing else is pulling it back. Yes, they say, the cart is pulling back. But what is it pulling back? Not itself, Shirley. No, the horse. Yes, certainly the cart is pulling at the horse. If the cart offered no resistance, what would be the good of the horse? That is what he's for, to overcome the pullback of the cart. But nothing is pulling the cart back, except of course a little friction. And the horse is pulling it forward, hence it goes forward. There's no puzzle at all when once you realize that there are two bodies and two forces acting, and that one force acts on each body. If indeed two balanced forces acted on one body, that would be an equilibrium. But the two equal forces contemplated in the third law act on two different bodies, and neither is an equilibrium. So much for the third law, which is extremely simple. Though it is extraordinarily far-reaching consequences, and when combined with a denial of action at a distance, is precisely the principle of the conservation of energy. Attempts at perpetual motion may all be regarded as attempts to get around this third law. On the subject of the second law, a great deal more has to be said before it can be, in any proper sense, even partially appreciated. But a complete discussion of it would involve a treatise on mechanics. It is the law of mechanics. One aspect of it we must attend to now in order to deal with the motion of the planets, and that is the fact that the change of motion of a body depends solely and simply on the force acting, and not at all upon what the body happens to be doing at the time it acts. It may be stationary, or it may be moving in any direction, that makes no difference. Thus referring back to the Summary Proceeding Lecture 4. It is there stated that a dropped body falls 16 feet in the first second, that in two seconds it falls 64 feet, and so on, in proportion to the square of the time. So also will it be the case with a thrown body? But the drop must be reckoned from its line of motion, the straight line which, but for gravity it would describe. Thus the stone thrown from O with the velocity, the product of O and A, would in one second find itself at A, and two seconds at B, and three seconds at C, and so on, in accordance with the first law of motion, if no force acted. But if gravity acts, it will have fallen 16 feet by the time it would have got to A, and so will find itself at P. In two seconds it will be at Q, having fallen a vertical height of 64 feet, and three seconds it will be at R, 144 feet below C, and so on. Its actual path will be a curve, which in this case is a parabola. If a cannon is pointed horizontally over a level plane, the cannon ball will be just as much affected by gravity as if it were dropped, and so will strike the plane at the same instance as another which was simply dropped where it started. One ball may have gone a mile, and the other only dropped a hundred feet or so. But the time needed by both the vertical drop will be the same. The horizontal motion of one is an extra, and is due to the powder. As a matter of fact the path of projectile in vacuo is only approximately a parabola. It is instructive to remember that it is really an ellipse with one focus very distance, but not at infinity. One of its foci is the center of the earth, a projectile is really a minute satellite of the earth, and in vacuo it accurately obeys all Kepler's laws. It happens not to be able to complete its orbit because it was started inconveniently close to the earth, whose bulk gets in its way. But in that respect the earth is to be reckoned as a gratuitous obstruction, like a target, but a target that differs from most targets in being hard to miss. Now consider circular motion in the same way. Say a ball world round by a string. Attending to the body at O, it is for an instant moving towards A, and if no force acted it would get to A, in a time which for brevity we may call a second. But a force, the pull of the string, is continually drawing it towards S, and so it really finds itself at P, having described circular arc OP, which may be considered to be compounded of and analyzable into the rectilinear motion OA and the drop AP. At P it is for an instant moving towards B, and the same process therefore carries it to Q, and the third second it gets to R, and so on. Always following, so to speak, from its natural rectilinear path towards the center, but never getting any nearer to the center. The force with which it has thus to be constantly pulled in towards the center, or which is the same thing, the force with which it is tugging at whatever constraint it is that holds it in, is the product of M and V squared divided by R, where M is the mass of the particle, the mass of its velocity, and are the radius of its circle of movement. This is the formula first given by Hagen's for centrifugal force. We may find it convenient to express it in terms of the time of the One Revolution, say capital T. It is easily done since plainly capital T equals circumference divided by speed, which equals the product of 2 pi R divided by V. So the above expression for centrifugal force becomes the product 4 pi squared MR divided by capital T squared. As to the fall of the body towards the center, every microscopic unit of time is easily reckoned for by Euclid 3 36 and figure 58 AP A A prime equals A O squared. Take A very near O then A O equals VT and A A prime equals 2 R so AP equals the product of V squared and T squared divided by 2 R, which equals the product of 2 pi squared R T squared divided by capital T squared. For the fall per second is the product of 2 pi squared R divided by capital T squared. R being its distance from the center in capital T it's time of going once round. In the case of the moon for instance, R is 60 Earth radii more exactly 60.2 and capital T is a lunar month or more precisely 27 days 7 hours 43 minutes and 11 and a half seconds. Hence the moon's deflection from the tangential or rectilinear path every minute comes out as very closely 16 feet the true size of the Earth being used. Returning now to the case of a small body revolving around a big one and assuming a force directly proportional to the mass of both bodies and then inversely proportional to the square of the distance between them and the known force of gravity it is the product of gamma capital M and M divided by R squared or gamma is a constant called the gravitational constant to be determined by experiment. If this is the centripetal force pulling a planet or satellite in it must be equal to the centrifugal force of this ladder. These, the product of 4 pi squared M R divided by capital T squared equate the two together and at once we get divided by capital T squared equals gamma divided by 4 pi squared times capital M or in the words the cube of the distance divided by the square of the periodic time for every planet or satellite of the system under consideration will be constant and proportional to the mass of the central body. This is Kepler's third law with a notable addition. It is stated above for circular motion only so as to avoid geometrical difficulties but even so it is very instructive The reason of this proportion between R cubed and capital T squared is at once manifest and as soon as the constant gamma became known the mass of the central body the sun in the case of a planet the earth in the case of the moon Jupiter in the case of his satellites was at once determined. Newton's reasoning at this time might however be better displayed perhaps by altering the order of these steps a little as thus the centrifugal force of a body is proportional to R cubed divided by capital T squared but by Kepler's third law R cubed divided by capital T squared is constant for all planets reckoning R from the sun hence the centripetal force needed to hold in all the planets will be a single force emanating from the sun and varying inversely with the square of the distance from that body Such a force is at once necessary and sufficient. Such a force would explain the motion of the planets but then all this proceeds on a wrong assumption that the planetary motion is circular until it holds for elliptic orbits Will an inverse square law of force keep a body moving in an elliptic orbit or vell the sun in one focus? This is a far more difficult question Newton solved it but I do not believe that even he could have solved it except that he had at his disposal two mathematical engines of great power the Cartesian method of treating geometry and his own method of fluxions One can explain the elliptic motion now mathematically but hardly otherwise and I must be content to state that the devil fact is true V's that an inverse square law will move the body in an ellipse or other conic section with the sun in one focus and that if a body so moves it must be acted on by an inverse square law This then is the meaning of the first and third laws of Kepler What about the second? What is the meaning of the equable description of areas? Well that rigorously proves that a planet is acted on by a force and that our description of area is equable It proves in fact that the sun is the attracting body and that no other force acts But first of all if the first law of motion is obeyed i.e. if no force acts and if the path be equally subdivided to represent equal times and straight lines be drawn from the divisions to any point whatever all these areas thus enclosed will be equal because they are triangles on equal base and of the same height whatever in A, B, C successive positions of a body Now at each of the successive instance let the body receive a sudden blow in the direction of that same point S sufficient to carry it from A to D in the same time as it would have got to B if left alone The result will be that there will be a compromise and it will really arrive at P traveling along the diagonal of the parallelogram AP The area its radius vector sweeps out or sap instead of what it would have been sab But then these two areas are equal because they are triangles on the same base AS and between the same parallels BP, AS for by the parallelogram law BP is parallel to AD hence the area that would have been described is described and as all the areas were equal in the case of no force they remain equal when the body receives a blow at the end of every equal interval of time provided that every blow is actually directed to S the point to which radii vectors are drawn It is instructive to see that it does not hold if the blow is any otherwise directed for instance as in figure 61 when the blow is along AE the body finds itself at P at the end of the second interval but the area sap is by no means equal to sap and therefore not equal to SOA the area swept out in the first interval in order to modify figure 60 so as to represent continuous motion and steady forces we have to take the sides of the polygon OAPQ very numerous and very small in the limit infinitely numerous and infinitely small the path then becomes a curve and the series of blows becomes a steady force directed towards S about whatever point therefore the rate of description of areas is uniform that point in no other must be the center of all the force there is if there be no force as in figure 59 but if there be any force however small not directed towards S then the rate of description of areas about S cannot be uniform Kepler however says that the rate of description of areas of each planet about the sun is by Tycho's observations uniform hence the sun is the center of all the force that acts on them and there is no other force not even friction that is the moral of Kepler's second law we may also see from it that gravity does not travel like light time on its journey from sun to planet for if it did there would be a sort of aberration and the force on its arrival could no longer be accurately directed to the center of the sun see nature volume 46 page 497 it is a matter for accuracy of observation therefore to decide whether the minutest trace of such deviation can be detected i.e. within what limits of accuracy Kepler's second law is now known to be obeyed I will content myself by saying that the limits are extremely narrow reference may be made also to page 208 thus then it became clear to Newton that the whole solar system depended on a central force emanating from the sun and varying inversely with the square of the distance from him for by that hypothesis all the laws of Kepler concerning these motions were completely accounted for and in fact the laws necessitated the hypothesis and established it as in theory similarly the satellites of Jupiter controlled by a force emanating from Jupiter and varying according to the same law and again our moon must be controlled by a force from the earth decreasing with the distance according to the same law grant this hypothetical attracting force pulling the planets towards the sun pulling the moon towards the earth and the whole mechanism of the solar system is beautifully explained if only one could be sure there was such a force it was one thing to calculate out what the effects of such a force would be it was another to be put one's finger upon it and say this is the force that actually exists and is known to exist we must picture him meditating in the garden on this want an attractive force towards the earth if only such an attractive force pulling down bodies to the earth existed an apple falls from a tree why it does exist there is gravitation common gravity that makes bodies fall and gives them their weight wanted a force tending towards the center of the earth and it is common old gravity that has been known so long that was perfectly familiar to Galileo and probably to Archimedes gravity that regulates the motion of projectiles why should it only pull stones and apples why should it not reach as high as the moon why should it not be the gravitation of the sun that is the central force acting on all the planets surely the secret of the universe is discovered but wait a bit is it discovered is this force of gravity sufficient for the purpose it must vary inversely with the square of the distance from the center of the earth how far is the moon away sixty earth radii hence the force of gravity at the moon's distance can only be one thirty six hundredth of what it is on the earth's surface so instead of pulling it sixteen feet per second it should pull it sixteen thirty six hundredths feet per second or sixteen feet a minute how can one decide whether such a force is able to pull the moon the actual amount required and this would seem only like a sum in arithmetic out with the pencil and paper and reckon how much the moon falls towards the earth in every second of its motion is it sixteen thirty six hundredths that is what it ought to be but is it the size of the earth comes into the calculation sixty miles makes a degree three hundred sixty degrees is a conference this gives as the earth's diameter six thousand eight hundred seventy three miles work it out the answer is not sixteen feet a minute it is thirteen point nine feet surely a mistake of calculation no it is no mistake there is something wrong in the theory gravity is too strong instead of falling towards the earth five and a third hundredths of an inch every second as it would under gravity the moon only falls four and two third hundredths of an inch per second with such a discovery in his grasp at the age of twenty three he is disappointed the figures do not agree and he cannot make them agree it is not the force in action or else something interferes with it possibly gravity does part of the work and the vortices of Descartes interfere with it he must abandon the fascinating idea for the time in his own words he laid aside at that time any further thought of the matter so far as it is known he never mentioned his disappointment to his soul he might perhaps if he had been at Cambridge but he was a shy and solitary youth and just as likely he might not up in Lincolnshire in the seventeenth century for him to consult true he might have rushed into a premature publication after our nineteenth century fashion but that was not his method publication never seemed to have occurred to him his reticence now is noteworthy but later on it is perfectly astonishing he is so absorbed in making discoveries that he actually has to be reminded to tell anyone about them and someone else always has to see to the printing and publishing for him I have entered thus fully into what I conjectured to be the stages of this early discovery about gravitation as applicable to the heavenly bodies because it is frequently and commonly misunderstood it is sometimes thought that he discovered the force of gravity I hope I have made it clear that he did no such thing every educated man long before his time if asked why bodies fell would reply just as glibly as they do now because the earth attracts them or because of the force of gravity his discovery was that the motions of the solar system were due to the action of a central force of the whole body at that center of the system and varying inversely with the square of the distance from it this discovery was based upon Kepler's laws it was clear and certain it might have been published had he so chosen but he did not like hypothetical and unknown forces he tried to see whether the known force of gravity would serve this discovery at that time he failed to make owing to a wrong numerical datum the size of the earth he only knew from the common doctrine of sailors that 60 miles make a degree he threw him out instead of falling 16 feet a minute as it ought under gravity it only fell 13.9 feet so he abandoned the idea we do not find that he returned to it for 16 years end of lecture 7 lecture 8 of pioneers of science this is a LibriVox recording all LibriVox recordings are in the public domain for more information or to volunteer please visit LibriVox.org pioneers of science by Sir Oliver Lodge lecture 8 Newton and the law of gravitation we left Newton at the age of 23 on the verge of discovering the mechanism of the solar system deterred there from only by an error in the then imagined size of the earth he had proved from Kepler's laws that the centripetal force directed to the sun and varying as the inverse square of the distance from that body would account for the observed planetary motions and that a similar force directed to the earth would account for the lunar motion and it had struck him that this force might be the very same as the familiar force of gravitation which gave to bodies their weight but in attempting a numerical verification of this idea in the case of the moon he was led by the then received notion that 60 miles made a degree on the earth's surface into an erroneous estimate of the size of the moon's orbit being thus baffled in obtaining such verification he laid the matter aside for a time the anecdote of the apple we learned from Voltaire who had it from Newton's favorite niece who with her husband lived and kept house for him all his later life it is very like one of those anecdotes which are easily invented and believed in and very often turn out on scrutiny to have no foundation fortunately this anecdote is well authenticated and moreover is intrinsically probable I say fortunately because it is always painful to have to give up these child learned anecdotes like Alfred in the cakes and so on this anecdote of the apple we need not resign the tree was blown down in 1820 and part of its wood is preserved in Voltaire in connection with Newton's philosophy this acute critic at a later stage did a good deal to popularize it throughout Europe and to overturn that it was own countryman Descartes Cambridge rapidly became Newtonian but Oxford remained Cartesian for 50 years or more it is curious what little hold science and mathematics have ever secured in the older and more ecclesiastical university the pride of possessing Newton there were no doubt been the main stimulus to the special pursuits of Cambridge he now began to turn his attention to optics and as was usual with him his whole mind became absorbed in this subject as if nothing else had ever occupied him his cash book for this time had been discovered and the entries show that he is buying prisms and lenses and polishing powder at the beginning of 1667 he was anxious to improve telescopes than had ever been used before accordingly he calculated out their proper curves just as Descartes had also done and then proceeded to grind them as near as he could to those figures but the images did not please him they were always blurred and rather indistinct at length it struck him that perhaps it was not the lenses but the light which was at fault perhaps light was so composed that it could not be focused accurately at a definite point perhaps the law of refraction was not quite accurate but only in approximation so he bought a prism to try the law he let the sunlight through a small round hole in a window shutter and served the prism in the light and received the deflected beam on a white screen turning the prism about till it was deviated as little as possible the patch on the screen was not a round disc as it would have been without the prism it was an elongated oval and was colored at its extremities evidently refraction was not a simple geometrical deflection of array there was a spreading out as well why did the image thus spread out if it were due to irregularities in the glass a second prism should rather increase them but a second prism when held in appropriate position was able to neutralize the dispersion and to reproduce the simple round white spot of the radiation evidently the spreading out of the beam was connected in some definite way with its refraction could it be that the light particles after passing through the prism traveled in variously curved lines as spinning racquet balls do to examine this he measured the length of the oval patch when the screen was at different distances from the prism and found that the two things were directly proportional to each other doubling the distance of the screen hence the rays traveled in straight lines from the prism and the spreading out was due to something that occurred within its substance could it be that white light was compound was a mixture of several constituents and that its different constituents were differently bent no sooner thought than tried pierce the screen to let one of the constituents through and interpose a second prism in its path if the spreading out depended on the prism only it should spread out just as much as before but if it depended on the complex character of white light this isolated simple constituent should be able to spread out no more it did not spread out anymore a prism had no more dispersive power over it it was deflected by the appropriate amount but it was not analyzed into constituents it differed from sunlight in being simple with many ingenious and beautifully simple experiments which are quoted in full and several books on optics he clinched the argument and established his discovery white light was not simple but compound it could be sorted out by a prism into an infinite number of constituent parts which were differently refracted and the most striking of which Newton named violet, indigo, blue, green, yellow, orange and red at once the true nature of color became manifest color resided not in the colored object as had till now been thought in the light which illuminated it red glass for instance adds nothing to sunlight the light does not get dyed red by passing through the glass all that the red glass does is to stop and absorb a large part of the sunlight it is opaque to the larger portion but it is transparent to that particular portion which affects our eyes with the sensation of red the prism acts as a sieve sorting out the different kinds of light colored media act like filters stopping certain kinds but allowing the rest to go through Leonardo's and all the ancient doctrines of color had been singularly wrong color is not in the object but in the light Goethe in his Fabenlerre endeavored to contravert Newton and to reinstate something more like the old views but his failure was complete refraction analyzed out the various constituents of white light and displayed them in the form of a series of overlapping images of the aperture each of a different color this series of images we call a spectrum and the operation we now call spectrum analysis the reason of the defect of lenses was now plain it was not so much a defect in the lens as a defect of light a lens acts by refraction and brings rays into a focus if light be simple it acts well but if ordinary white light fall upon a lens its different constituents have different foci every bright object is fringed with color and nothing like a clear image can be obtained a parallel beam passing through a lens becomes conical but instead of a single cone it is a sheaf or nest of cones all having the edge of the lens as base but each having a different vertex the violet cone is innermost near the lens the red cone outermost others lie in between beyond the crossing point or focus the order of cones is reversed as the above figure shows only the two marginal rays of the beam are depicted if a screen be held anywhere nearer the lens than the place marked 1 there will be a whitish center to the patch of light and a red and orange fringe or border held anywhere beyond the region 2 the border of the patch will be blue the violet held about 3 the color will be less marked than elsewhere but nowhere can it be got rid of each point of an object will be represented in the image not by a point but by a colored patch a fact which amply explains the observed blurring and indistinctness Newton measured and calculated the distance between violet and red foci the R in the diagram and showed that it was with the diameter of the lens to overcome this difficulty called chromatic aberration telescope glasses were made small in a very long focus some of them so long that they had no tube all of them egregiously cumbers yet it was with such instruments that all the early discoveries were made with such an instrument for instance, Huygens discovered the real shape of Saturn's rings the defects of refractors seemed irremediable they were founded on the nature of light itself so he gave up his glassworks and proceeded to think of reflection from metal specula a concave mirror forms an image just as a lens does but since it does so without refraction or transmission through any substance there is no accompanying dispersion or chromatic aberration the first reflecting telescope he made was 1 inch diameter and 6 inches long and magnified 40 times it acted as well as a 3 or 4 feet refractor of that day and showed Jupiter's moons so he made a larger one now in the library of the Royal Society London with an inscription the first reflecting telescope invented by Sir Isaac Newton and made with his own hands this has been the parent of most of the gigantic telescopes of the present day 50 years elapsed before it was much improved on and then first by Hadley and afterwards by Herschel and others large and good reflectors were constructed the largest telescope ever made that of Lord Ross is a Newtonian reflector 50 feet long 6 feet diameter with a mirror weighing 4 tons the sextant, as used by navigators was also invented by Newton the year after the plague in 1667 Newton returned to Trinity College and there continued his experiments on optics it is specially to be noted that at this time at the age of 24 Newton had laid the foundations of all his greatest discoveries theory of fluctuations or the differential calculus the law of gravitation or the complete theory of astronomy the compound nature of white light or the beginning of spectrum analysis his later life was to be occupied in working these incipient discoveries out but the most remarkable thing is that no one knew about any one of them however he was known as an accomplished young mathematician and was made a fellow of his college he remembered that he had a friend there in the person of Dr. Isaac Barrow first location professor of mathematics in the university it happened about 1669 that a mathematical discovery of some interest was being much discussed and Dr. Barrow happened to mention it to Newton who said yes he had worked out that a few other similar things some time ago he accordingly went and fetched some papers to Dr. Barrow who forwarded them to other distinguished mathematicians and it thus appeared that Newton had discovered theorems much more general than this special case that was exciting so much interest Dr. Barrow being anxious to devote his time more particularly to theology resigned his chair the same year in favor of Newton who was accordingly elected the location professorship which he held for 30 years this chair is now the most famous in the university and is commonly referred to as the chair of Newton still however his method of fluctuations was unknown and still he did not publish it he lectured first on optics giving an account of his experiments his lectures were afterwards published both in Latin and English and are highly valued to this day the fame of his mathematical genius came to the ears of the royal society and a motion was made to get him elected a fellow of that body the royal society the oldest and most famous of all scientific societies with a continuous existence took its origin in some private meetings got up in London by the honorable Robert Boyle and a few scientific friends during all the trouble of the Commonwealth after the restoration Charles II in 1662 incorporated it under the royal charter among the original members being Boyle Hooke, Christopher Wren and other less famous names Boyle was a great experimenter a worthy follower of Dr. Gilbert Hooke began as his assistant but being of a most extraordinary ingenuity he rapidly rose so as to exceed his master in importance fate has been a little unkind to Hooke in placing him so near to Newton had he lived in an ordinary age he would undoubtedly have shown as a star of the first magnitude great ingenuity remarkable scientific insight and consummate experimental skill he stands in many respects almost on a level with Galileo but it is difficult to see stars even of the first magnitude when the sun is up and thus it happens that the name and fame of this brilliant man are almost lost in the blaze of Newton of Christopher Wren I need not say much he is well known as an architect but he was a most accomplished all round man and had a considerable taste in faculty for science these then were the luminaries of the Royal Society at the time we are speaking of and to them Newton's first scientific publication was submitted he communicated to them an account of his reflecting telescope and presented them with the instrument the reception of it surprised him they were greatly delighted with it and wrote specially thanking him for the communication and assuring him that all right should be done him in the matter of the invention of Charlesbury Bishop Burnett proposed him for election as a fellow and elected he was in reply he expressed a surprise at the value they said on the telescope and offered, if they cared for it to send them an account of a discovery which he doubts not will prove much more grateful than the communication of that instrument quote being in my judgment the oddest if not the most considerable detection that has recently been made of the interpretations of nature unquote so he tells them about his optical researches and his discovery of the nature of white light writing them a series of papers which were long afterwards incorporated and published as his optics a magnificent work which of itself suffices to place its author in the first rank of the world's men of science the nature of white light the true doctrine of color of the resulting telescope sextant and the like one would think it enough for one man's life work but the masterpieces remain still to be mentioned it is as when one is considering Shakespeare King Lear Macbeth a fellow surely a sufficient achievement but the masterpiece remains comparisons in different departments are but little help perhaps nevertheless it seems to me that in his own department science Newton towers head and shoulders over not only his contemporaries that is a small matter but over every other scientific man who has ever lived in a way that we can find no parallel for in other departments other nations admit his scientific preeminence with as much alacrity as we do well we have arrived at the year 1672 in his election to the royal society during the first year of his membership there there was read at one of the meetings of a very careful determination of the length of a degree i.e. of the size of the earth which had been made by Picard near Paris the length of the degree turned out to be not 60 miles but nearly 70 miles how soon Newton heard of this we do not learn probably not for some years Cambridge was not so near London then as it is now but ultimately it was brought to his notice armed with this new datum all speculation concerning gravity occurred to him he had worked out the mechanics of the solar system on a certain hypothesis but it remained a hypothesis somewhat out of harmony with the apparent fact what if it should turn out to be true after all he took out his old papers and began again the calculation if gravity were the force keeping the moon in its orbit it would fall toward the earth 16 feet every minute how far did it fall the newly known size of the earth would modify the figures with intense excitement he runs through the working his mind leaps before his hand and as he perceives the answer to be coming out right all the infinite meaning and scope of his mighty discovery flashes upon him and he can no longer see the paper he throws down the pen and the secret of the universe is to one man known but of course it had to be worked out the meaning might flash upon him but it's full detail required years of elaboration deeper and deeper consequences revealed themselves to him as he proceeded for two years he devoted himself solely to this one object during those years he lived but to calculate and think and the most ludicrous stories are told concerning his entire absorption and inattention to ordinary affairs of life thus for instance when getting up in a morning he would sit on the side of the bed half-dressed and remain like that till dinner time often he would stay at home for days together eating what was taken to him but without apparently noticing what he was doing one day an intimate friend Dr. Stucley called on him and found on the table a cover laid for his solitary dinner after waiting a long time Dr. Stucley removed the cover and ate the chicken underneath it replacing and covering up the bones again that length Newton appeared and after greeting his friends sat down to dinner upon lifting the cover he said in surprise, dear me I am not dying but I see I have it was by this continuous application that the Principia was accomplished probably nothing of the first magnitude can be accomplished without something of the same absorbed unconsciousness and freedom from interruption but though desirable and essential for the work it was a severe tax upon the powers of the man there is in fact no doubt that Newton's brain suffered temporary aberration after this effort for a short time the attack was slight and it has been denied but there are letters extant which are inexplicable otherwise and moreover after a year or two he writes to his friends apologizing for strange and disjointed epistles which he believed had been written without understanding clearly what he wrote the derangement was however both slight and temporary and it is only instructive to us showing at what cost such a work as the Principia must be produced even by so mighty a mind as that of Newton the first part of the work many ordinary mortal would have proceeded to publish it but the fact is that after he had sent to the Royal Society his papers on optics there had risen controversies and objections most of them rather paltry to which he felt compelled to find answers many men would have enjoyed this part of the work and taken it as evidence of interest and success but to Newton's shy and retiring disposition these discussions were merely painful he writes indeed his answers with great patience and ability and ultimately converts the more reasonable of his opponents but he relieves his mind in the following letter to the Secretary of the Royal Society quote I see I have made myself a slave to philosophy but if I get free of this present business I will resolutely bid adieu to it eternally except what I do for my private satisfaction I'll leave to come out after me for I see a man must either resolve to put out nothing new or to become a slave to defend it quote and again in a letter to Leipniz quote I have been so persecuted with discussions arising out of my theory of light that I blamed my own imprudence for parting with so substantial a blessing as my quiet to run after a shadow unquote this shows how much he cared for a contemporary fame so he locked up the first part of the Principia in his desk doubtless intending it to be published after his death but fortunately this was not to be so in 1683 among the leading lights of the royal society the same sort of notions about gravity and the solar system began independently to be brooded the theory of gravitation seemed to be in the air and Wren, Hook and Halley had many a talk about it Hook showed an experiment with a pendulum which he likened to a planet going around the sun the analogy is more superficial than real it does not obey Kepler's laws still it was a striking experiment they had guessed at a law of inverse squares and their difficulty was to prove what curve a body subject to it would describe they knew it ought to be an ellipse if it was to serve to explain the planetary motion and Hook said he could prove that an ellipse it was but he was nothing of a mathematician and the others scarcely believed him undoubtedly he had shrewed inklings of the truth though his guesses were based on little else than a most sagacious intuition he surmised also that gravity was the force concerned and asserted that the path of an ordinary projectile was an ellipse like the path of a planet which is quite right in fact the beginnings of the discovery were beginning to dawn upon him in the well-known way in which things do dawn upon ordinary men of genius and had Newton not lived the adventures of a long chain of distinguished men beginning with Hook, Ren and Halley have been now in possession of all the truths revealed by the Principia we should never have had them stated in the same form nor proved with the same marvelous lucidity and simplicity but the facts themselves we should by this time have arrived at their developments and completions due to such men as Clairot Euler, D'Alembert Lagrange, Laplace Laverrier, Adams we should of course not have had to the same extent because the lives and energies of these great men would have been partially consumed in obtaining the main facts themselves the youngest of the three questioners at the time we are speaking of was Edmund Halley an able and a remarkable man he had been at Cambridge doubtless had heard Newton lecture and had acquired a great veneration for him in February 1684 we find Ren offering Hook and Halley a prize in the shape of a book worth 40 shillings if they would either of them bring him within two months a demonstration that the path of a planet subject to an inverse square law would be an ellipse not in two months nor yet in seven was there any proof forthcoming so at last in August Halley went over to Cambridge to speak to Newton about the difficult problem and secure his aid in the rooms he went straight to the point he said what path will a body describe if it be attracted by a center with a force varying as the inverse square of the distance to which Newton at once replied an ellipse how on earth do you know said Halley an amazement why I have calculated it and began hunting about for the paper he actually couldn't find it just then but sent it him shortly by post on motion in general with his valuable burden Halley hastened to the Royal Society and told them what he had discovered the society at his representation wrote to Mr. Newton asking leave that it might be printed to this he consented but the Royal Society wisely appointed Mr. Halley to see after him and jog his memory in case he forgot about it however he set to work to polish it up and finish it and added to it a number of later developments and embellishments especially the part concerning the lunar theory which gave him a deal of trouble and no wonder for in the way he has put it there never was a man yet living who could have done the same thing mathematicians regard the achievement now as men might steer at the work of some demigod of a bygone age wondering what manner of man this was able to wield such ponderous implements with such apparent ease to Halley the world owes a great debt of gratitude first for discovering the Principia second for seeing it through the press and third for defraying the cost of its publication out of his own scanty purse for though he ultimately suffered no pecuniary loss rather the contrary yet there was considerable risk in bringing out a book which not a dozen men living could at the time comprehend it is no small part of the merit of Halley that he recognized the transcendent value of the yet unfinished work that he brought it to light and assisted in its becoming understood to the best of his ability though Halley afterwards became astronomer royal lived to the ripe old age of eighty six and made many striking observations yet he would be the first to admit that nothing he ever did was at all comparable in importance to his discovery of the Principia and he always used to regard his part in it with peculiar pride and pleasure and how was the Principia received considering the abstruse nature of its subject it was received with great interest and enthusiasm in less than twenty years the edition was sold out and copies fetched large sums we hear of poor students copying out the whole in manuscript in order to possess a copy not by any means a bad thing to do however many copies one may possess the only useful way really to read a book like that is to pour every sentence it is no book to be skimmed while the Principia was preparing for the press a curious incident of contact between English history and the university occurred it seems that James the second in his policy of Catholicize in the country ordered both universities to elect certain priests to degrees without the ordinary oaths Oxford had given away and the Dean of Christ Church was a creature of James Cambridge rebelled and sent eight of its members among them Mr. Newton to plead their cause before the court of High Commission Judge Jeffries presided over the court and threatened and bullied with his usual insolence the vice chancellor of Cambridge was deprived of office the other deputies were silenced and ordered away from the precincts of this court of justice Newton returned to Trinity College to complete the Principia by this time Newton was only 45 years old but his main work was done his method of fluctuations was still unpublished his optics was published only imperfectly a second edition of the Principia with additions and improvements had yet to appear but fame had now come upon him and with fame worries of all kinds by some fatality principally no doubt because of the interest they excited every discovery he published was the signal for an outburst of criticism and sometimes of attack I shall not go into these matters they are now trivial enough but it is necessary to mention them because to Newton they evidently loomed large and terrible and occasioned him to acute torment no sooner was the Principia put than hook put in his claims for priority and indeed his claims were not altogether negligible for vague ideas of the same sort had been floating in his comprehensive mind he felt indistinctly conscious of a great deal more than he could really state or prove by indiscreet friends these two great men were set somewhat at loggerheads and worse might have happened had they not managed to come to close quarters and correspond privately in a quite friendly manner instead of acting through the mischievous medium of third parties in the next edition Newton liberally recognizes the claims of both hook and wren however he takes warning of what he has to expect and writes to Halley that he will only publish the first two books those containing general theorems on motion the third book concerning the system of the world i.e. the application to the solar system he says I now design to suppress philosophy is such an impertinently litigious lady that a man had as good be engaged in lawsuits as have to do with her I found it so formally sooner come near her again but she gives me warning the two books without third will not so well bear the title mathematical principles of natural philosophy and therefore I had altered it to this on the free motion of two bodies but on second thoughts I retain the former title will help the sales of the book which I ought not to diminish now it is yours unquote however fortunately Halley was able to prevail upon him to publish the third book also indeed the most interesting and popular of the three as it contains all the direct applications to astronomy of the truth established in the other two some years later when his method of fluctuations was published another and a worse controversy arose this time with Leibniz who had also independently invented the differential calculus it was not so well recognized then how frequently it happens that two men independently and unknowingly work at the very same thing at the same time the history of science is now full of such instances but then the friends of each accused the other of plagiarism I will not go into the controversy it is painful and useless it only served to embitter the later years of two great men and it continued long after Newton's death long after both their deaths it can hardly be called ancient history even now but fame brought other and less unpleasant distractions than controversies we are a curious practical and rather stupid people and our one idea of honoring a man is to vote for him in some way or other so they sent Newton to Parliament he went, I believe, as a wig but it is not recorded that he spoke it is in fact recorded that he was once expected to speak when on a royal commission about some question of chronometers but that he would not however I dare say he made a good average member then a little later it was realized that Newton was poor and he had to teach for his livelihood and that though the crown had continued his fellowship to him as location professor without the necessity of taking orders yet it was rather disgraceful that he should not be better off so an appeal was made to the government on his behalf and Lord Halifax, who exerted himself strongly in the matter, succeeding to office on the accession of William III was able to make him ultimately master of the mint with a salary of some 1,200 pounds a year I believe he made rather a good master and turned out excellent coins certainly he devoted his attention to his work there in a most exemplary manner but what a pitiful business it all is here is a man sent by heaven to do certain things which no man else could do and so long as he is comparatively unknown he does them but so soon as he is found out he is clapped into a routine office with a big salary and there is comparatively speaking an end of him it is not to be supposed that he had lost his power for he frequently solved problems very quickly which had been given out by great continental mathematicians as a challenge to the world we may ask why Newton allowed himself to be thus bandied about instead of settling himself down to the work in which he was so preeminently great well I expect your truly great man never realizes how great he is and seldom knows where his real strength lies certainly Newton did not know it he several times talks of giving up philosophy altogether and though he never really does it and perhaps the feeling is one only born of some temporary overwork yet he does not sacrifice everything else to it as he surely must had he been conscious of his own greatness no self-consciousness was the last thing that affected him it is for a great man's contemporaries to discover him to make much of him and to put him in surroundings where he may flourish luxuriously in his own heaven intended way however it is difficult for us to judge of these things perhaps if he had been maintained at the national expense to do that for which he was preternaturally fitted he might have worn himself out prematurely whereas by giving him routine work the scientific world got the benefit of his matured wisdom and experience it was no small matter to the young royal society to be able to have him as their president for twenty four years the portrait has hung over the president's chair ever since and there I suppose it will continue to hang until the royal society becomes extinct the events of his later life I shall pass over lightly he lived a calm benevolent life universally respected and beloved his silver white hair when he removed his parook was a venerable spectacle a lock of it is still preserved with many other relics in the library of trinity college he died quietly after a painful illness at the ripe age of eighty-five his body lay in state in the Jerusalem chamber and he was buried in Westminster Abbey six peers bearing the pall these things ought to be mentioned to the credit of the time in the country for after we have seen the calamitous spectacle of the way Tycho and Kepler and Galileo were treated by their ungrateful and unworthy countries it is pleasant to reflect that England with all its mistakes recognized her great man when she received him and honored him with the best she knew how to give concerning his character one need only say that it was what one would expect and wish it was characterized by a modest calm dignified simplicity he lived frugally with his niece and her husband Mr. Conduit who succeeded him as master of the mint he never married nor apparently did he ever think of doing so the idea perhaps did not naturally occur to him any more than the idea of publishing his work did he was always a deeply religious man and a sincere Christian though somewhat of the Arian or Unitarian persuasion so at least it is asserted by orthodox divines who understand these matters he studied theology more or less all his life and towards the end was greatly interested in questions of biblical criticism and chronology by some ancient eclipse or other he altered the recognized system of dates a few hundred years and his book on the prophecies of Daniel and the revelation of St. John wherein he identifies the beast with the church of Rome and quite the orthodox way is still by some admired but in all these matters it is probable that he was a merely ordinary man with natural acumen and ability doubtless but nothing in the least superhuman in science the impression he makes upon me is only expressible by words inspired superhuman and yet if one realizes his method of work and the calm uninterrupted flow of all his earlier life perhaps his achievements become more intelligible when asked how he made his discoveries he replied quote by always thinking unto them I keep the subject constantly before me and wait till the first donnings open slowly by little and little into a full and clear light unquote that is the way quiet steady continuous thinking uninterrupted and unharassed brooding much may be done under those conditions much ought to be sacrificed to obtain those conditions all the best thinking work of the world has thus been done Buffon said genius is patience so says Newton quote if I have done the public any service this way it is due to nothing but industry and patient thought unquote genius patience? no it is not quite that or rather it is much more than that but genius without patience is like fire without fuel it will soon burn itself out End of lecture 8