 SECTION 64 OF A NEW PROPERTY IN THE AIR AND SEVERAL ETHER TRANSPARENT MEDIUMS NAMED INFLECTION. 2. Having therefore made it probable at least that the morning and evening redness may partly proceed from this inflection or refraction of the rays, we shall next show how the oval figure will be likewise easily deduced. Suppose we therefore EFGH in the sixth figure of the thirty-seventh scheme to represent the earth. A B C D the atmosphere, E I and E L two rays coming from the sun, the one from the upper, the other from the nether limb, these rays being by the atmosphere inflected appear to the eye at E, as if they had come from the points N and O, and because the ray L has a greater inclination upon the inequality of the atmosphere than I. Therefore must it suffer greater inflection and consequently to be further elevated above its true place than the ray I, which has a less inclination will be elevated above its true place. Once it will follow that the lower side appearing nearer the upper, than really it is, and the two lateral sides, vis, the right and left side, suffering no sensible alteration from the inflection, at least what it does suffer does rather increase the visible diameter than diminish it, as I shall show by and by. The figure of the luminous body must necessarily appear somewhat elliptical. This will be more plain if in the seventh figure of the thirty-seventh scheme we suppose A B to represent the sensible horizon, C D E F the body of the sun really below it, G H I K the same appearing above it elevated by the inflection of the atmosphere. Or if according to the best observation we make the visible diameter of the sun to be about three or four and thirty minutes, and the horizontal refraction according to Tycho be there about or somewhat more, the lower limb of the sun E will be elevated to I. But because by his account the point C will be elevated but twenty-nine minutes, as having not so great an inclination upon the inequality of the air, therefore I G which will be the apparent refracted perpendicular diameter of the sun will be less than C G, which is but twenty-nine minutes and consequently six or seven minutes shorter than the unreflacted apparent diameter. The parts D and F will be likewise elevated to H and K whose refraction by reason of its inclination will be bigger than that of the point C, though less than that of E. Therefore will the semi-diameter I L be shorter than L G, and consequently the underside of the appearing sun more flat than the upper. Now because the rays from the right and left sides of the sun, etc., have been observed by Rikiola and Grimaldus to appear more distant one from another than really they are, though by very many observations that I have made for that purpose with a very good telescope fitted with a divided ruler, I could never perceive any great alteration. Yet there being really some, it will not be amiss to show that this also proceeds from the refraction or inflection of the atmosphere. And this will be manifest if we consider the atmosphere as a transparent globe, or at least a transparent shell encompassing an opacious globe, which being more dense than the medium encompassing it, refracts or inflects all the entering parallel rays into a point or focus so that wheresoever the observer is placed within the atmosphere between the focus and the luminous body, the lateral rays must necessarily be more converged towards his eye by the refraction or inflection than they would have been without it, and therefore the horizontal diameter of the luminous body must necessarily be augmented. This might be more plainly manifest to the eye by the sixth figure. But because it would be somewhat tedious, and the thing being obvious enough to be imagined by anyone that attentively considers it, I shall rather omit it and proceed to show that the massive air near the surface of the earth consists or is made up of parcels, which do very much differ from one another in point of density and rarity, and consequently the rays of light that pass through them will be variously inflected, here one way, and there another, according as they pass so or so through those differing parts, and those parts being always in motion either upwards or downwards, or to the right or left, or in some way compounded of these, they do by this their motion inflect the rays, now this way, and presently that way. This irregular unequal and unconstant inflection of the rays of light is the reason why the limb of the sun, moon, Jupiter, Saturn, Mars, and Venus appear to wave, or dance, and why the body of the stars appear to tremulate or twinkle. Their bodies by this means being sometimes magnified and sometimes diminished, sometimes elevated, otherwise depressed, now thrown to the right hand and then to the left. And that there is such a property or unequal distribution of parts is manifest from the various degrees of heat and cold that are found in the air. From whence will follow a differing density and rarity both as to quantity and refraction, and likewise from the vapors that are interposed, which, by the way, I imagine as to refraction or inflection to do the same thing as if they were rarefied air, and that those vapors that ascend are both lighter and less dense than the ambient air which boils them up, and that those which descend are heavier and more dense. The first of these may be found true if you take a good thick piece of glass and heating it pretty hot in the fire, lay it upon such another piece of glass or hang it in the open air by a piece of wire, then looking upon some far distant object such as a steeple or tree, so as to raise from that object past directly over the glass before they enter your eye, you shall find such a tremulation and wavering of the remote object as will very much offend your eye. The like tremulous motion you may observe to be caused by the ascending streams of water in the like. Now from the first of these it is manifest that from the rarefaction of the parts of the air by heat, there is caused a differing refraction, and from the ascension of the more rarefied parts of the air which are thrust up by the colder, and therefore more condensed and heavy, is caused an undulation or wavering of the object, for I think that there are very few will grant that glass by as gentle a heat as may be endured by one's hand should send forth any of its parts and steams or vapors which does not seem to be much wasted by that violent fire of the green glass-house. But if yet it be doubted, let experiment be further made with that body that is accounted by chemists and others, the most ponderous and fixed in the world, for by heating of a piece of gold and proceeding in the same manner you may find the same effects. This trembling and shaking of the rays is more sensibly caused by an actual flame, or quick fire, or anything else heated glowing hot as by a candle, live coal, red hot iron or piece of silver, and the like. The same also appears very conspicuous if you look at an object betwixt which, and your eye, the rising smoke of some chimney is interposed, which brings into my mind what I had once the opportunity to observe, which was the sun rising to my eye just over a chimney that sent forth a copious steam of smoke. And taking a short telescope which I had then by me, I observed the body of the sun, though it was but just peeped above the horizon, to have its underside not only flatted and pressed inward, as it usually is when near the earth, but to appear more pertuberant downwards than if it had suffered no refraction at all. And besides all this the whole body of the sun appeared to tremble, or dance, and the edges are limbed to be very ragged or indented, undulating or waving much in the manner of a flag in the wind. As I have likewise often observed in a hot, sunshiny summer's day that looking on an object over a hot stone, or dry hot earth, I have found the object to be undulated or shaken much after the same manner. And if you look upon any remote object through a telescope, in a hot summer's day especially, you shall find it likewise to appear tremulous. And further if there are chance to blow any wind, or that the air between you and the object be an emotion or current whereby the parts of it, both rarified and condensed, are swiftly removed towards the right or left, if then you observe the horizontal ridge of a hill far distant through a very good telescope, you shall find it to wave much like the sea, and those waves will appear to pass the same way with the wind. From which in many other experiments it is clear that the lower region of the air, especially that part of it which lieth nearest to the earth, has for the most part its constituent parcels variously agitated, either by heat or winds, by the first of which some of them are made more rare, and so suffer a less refraction. Others are interwoven, either with ascending or descending vapours, the former of which, being more light, and so more rarified, have likewise a less refraction. The latter being more heavy and consequently more dense, have a greater. Now because that heat and cold are equally diffused every way and that the further it is spread the weaker it grows, hence it will follow that the most part of the under-region of the air will be made up of several kinds of lenses, some more of will have the properties of confects, others of concave glasses, which that I may the more intelligibly make out we will suppose in the eighth figure of the thirty-seven scheme that A represents an ascending vapour which, by reason of its being somewhat heterogenous to the ambient air, is thereby thrust into a kind of globular form, not anywhere terminated but gradually finished, that is it is most rarified in the middle about A, somewhat more condensed about B.B., more than that about C.C., yet further about D.D., almost of the same density with the ambient air about E.E. and lastly enclosed with the more dense air F.F., so that from A to F.F. there is a continual increase of density, the reason of which will be manifest if we consider the rising vapour to be much warmer than the ambient heavy air, for by the coldness of the ambient air the shell E.E. will be more refrigerated than D.D., and that than C.C., which will be yet more than B.B., and that more than A., so that from F to A. there is a continual increase of heat, and consequently of rarity. From whence it will necessarily follow that the rays of light will be inflected or refracted in it, in the same manner as they would be in a concave glass? For the rays G.K.I., G.K.I. will be inflected by G.K.H., G.K.H., which will easily follow from what I before explained concerning the inflection of the atmosphere. While the other side of descending vapour, or any part of the air included by an ascending vapour, will exhibit the same effects with a convex lens. For if we suppose in the former figure the quite contrary constitution to that last described, that is the ambient air F.F. being hotter than any part of that matter within any circle, therefore the coldest part must necessarily be A., as being farthest removed from the heat, all the intermediate spaces will be gradually discriminated by the continual mixture of heat and cold, so that it will be hotter at E.E. than D.D., in D.D. than C.C., in C.C. than B.B., and in B.B. than A., from which a light refraction and condensation will follow, and consequently a lesser or greater refraction, so that every included part will refract more than the including, by which means the rays G.K.I., G.K.I. coming from a star or some remote object, are so inflected that they will again concur and meet in the point M. By the interposition thereof of this descending vapour, the visible body of the star or other object is very much augmented as by the former it was diminished. From the quick consecutions of these two, one after the other between the object and your eye, caused by their motion upwards or downwards, proceeding from their levity or gravity or to the right or left, proceeding from the wind, a star may appear, now bigger, now less, than really it would otherwise without them. And this is that property of a star which is commonly called twinkling or scintillation. The reason why a star will now appear of one color, now of another, which for the most part happens when tis near the horizon, may very easily be deduced from its appearing now in the middle of the vapour, otherwise near the edge, for if you look against the body of a star with a telescope that has a pretty deep convex eyeglass, and so order it that the star may appear sometimes in one place and sometimes in another of it, you may perceive this or that particular color to be predominant in the apparent figure of the star, according as it is more or less remote from the middle of the lens. This I could hear further explain, but that it does more properly belong to another place. I shall therefore only add some few queries which the consideration of these particulars hinted and so finish this section. And the first I shall propound is whether there may not be made an artificial transparent body of an exact globular figure that shall so inflect or refract all the rays that coming from one point fall upon any hemisphere of it, that every one of them may meet on the opposite side and cross one another exactly in a point, and that it may do the like also with all the rays that coming from a lateral point fall upon any other hemisphere, for if so there were to be hope to perfection of diopteryx, and a trans migration into heaven even whilst we remain here upon earth in the flesh, and a descending or penetrating into the center and innermost recesses of the earth, and all earthly bodies. Nay, it would open not only a cranny but a large window, as I may so speak, into the shop of nature whereby we might be enabled to see both the tools and operators in the very manner of the operation itself of nature. This, could it be affected, would as far surpass all other kinds of perspectives as the vast extent of heaven does the small point of the earth, which distance it would immediately remove and unite them as twer into one, at least that there should appear no more distance between them than the length of the tube into the ends of which these glasses should be inserted. Now whether this may not be affected with parcels of glass of several densities I have sometimes proceeded so far as to doubt. Though in truth as to the general I have wholly disparate of it, for I have often observed in optical glasses a very great variety of the parts, which are commonly called veins. Nay, some of them round enough, for they are for the most part drawn out into firings, to constitute a type of lens. This I should further proceed to hope had any one been so inquisitive as to have found out the way of making any transparent body either more dense or more rare, for then it might be possible to compose a globule that should be more dense in the middle of it than in any other part, and to compose the whole bulk so as that there should be a continual gradual transition from one degree of density to another such as should be found requisite for the desired inflection of the transmigrating rays. But of this enough at present, because I may say more of it when I set down my own trials concerning the mealieration of diopteryx, where I shall enumerate with how many several substances I have made both microscopes and telescopes, and by what and how many ways. Let us as have leisure and opportunity farther consider it. The next query shall be whether by the same collection of a more dense body than the other, or at least of the denser part of the other, there might not be imagined a reason of the apparition of some new fixed stars, as those in the swan, Cassiope's char, Serpentarius, Pisces, Cetus, etc. Thirdly whether it be possible to define the height of the atmosphere from this inflection of the rays or from the quicksilver experiment of the rarefication or extension of the air. Fourthly, whether the disparity between the upper and under air be not sometimes so great as to make a reflecting superfaces. I have had several observations which seem to have proceeded from some such cause, but it would be too long to relate and examine them. An experiment also somewhat analogous to this I have made with salt water and fresh, which two liquors in most positions seemed the same and not to be separated by any determinate superfaces, which separating surface yet in some other positions did plainly appear. And if so whether the reason of the equal bounding or terminus of the under parts of the clouds may not proceed from this cause, whether secondly the reason of the apparition of many suns may not be found out by considering how the rays of the sun may be so reflected as to describe a pretty true image of the body as we find them from any regular superfaces. But there also this may not be found to cause the apparition of some of these paralli of counterfeit suns which appear colored by refracting the rays so as to make the body of the sun appear in quite another place than really it is. But of this more elsewhere. Five. Whether the phenomena of the clouds may not be made out by this diversity of density in the upper and under parts of the air, by supposing the air above them to be much lighter than they themselves are, and they themselves to be yet lighter than that which is subjacent to them, many of them seeming to be the same substance with the cobwebs that fly in the air after a fog. Now that such a constitution of the air and clouds of such there be may be sufficient to perform this effect may be confirmed by this experiment. Make as strong a solution of salt as you are able. Then filling a glass of some depth half full with it. Fill the other half with fresh water and poise a little glass bubble so that it may sink pretty quick in fresh water which take and put into the aforesaid glass and you shall find it to sink till it comes towards the middle where it will remain fixed without moving either upwards or downwards. And by a second experiment of poising such a bubble in water whose upper part is warmer and consequently lighter than the under which is colder and heavier, the manner of which follows in this next query which is six. Whether the rarefication and condensation of water be not made after the same manner as those effects are produced in the air by heat, for I once poised a sealed up glass bubble so exactly that never so small an addition would make it sink, and as small a detraction make it swim which suffering to rest in that vessel of water for some time I always found it about noon to be at the bottom of the water, at night and in the morning at the top. Imagining this to proceed from the rarefication of the water caused by the heat I made trial and found most true for I was able at any time either to depress or raise it by heat and cold. For I let the pipe stand for some time in cold water I could easily raise the bubble from the bottom whither I had a little afford to truited it by putting the same pipe into warm water. And this way I have been able for a very considerable time to keep a bubble so poised in the water as that it should remain in the middle in neither sink nor swim. Pregently heating the upper part of the pipe with a candle, coal or hot iron till I perceived the bubble began to descend, then forbearing I have observed it to descend to such or such a station, and there to remain suspended for some hours till the heat by degrees were quite vanished when it would again ascend to its former place. This I have also observed naturally performed by the heat of the air which being able to verify the upper parts of the water sooner than the lower, by reason of its immediate contact the heat of the air has sometimes so slowly increased that I have observed the bubble to be some hours in passing between the top and bottom. 7. Whether the appearance of the Pike of Tenerife and several other high mountains at so much greater a distance than seems to agree with their respective heights be not attributed to the curvature of the visual ray that is made by passing obliquely through so differingly dense a medium from the top to the eye very far distant in the horizon. For since we have already, I hope, made it very probable that there is such an inflection of the rays by the differing density of the parts of the air, and since I have found by several experiments made on places comparatively not very high, and have yet found the pressure sustained by those parts of the air at the top and bottom, and also their differing expansions very considerable. In so much that I have found the pressure of the atmosphere lighter at the top of St. Paul's steeple in London, which is about two hundred foot high, then at the bottom by a sixtieth or fiftieth part, and the expansion at the top greater than at the bottom by near about so much also, for the mercurial cylinder at the bottom was about thirty-nine inches and at the top half an inch lower. The air also included in the weather glass that at the bottom filled only one hundred fifty-five spaces, at the top filled one hundred fifty-eight, though the heat at the top and bottom was found exactly the same with a scaled thermometer. I think it very rational to suppose that the greatest curvature of the rays is made nearest the earth, and that the inflection of the rays above, three or four miles upwards, is very inconsiderable, and therefore that by this means such calculations of the height of mountains is made from the distance they are visible in the horizon, from the supposal that that ray is a straight line, that from the top of the mountain is, as to our a tangent to the horizon whence it is seen, which really is a curve, is very erroneous, whence I suppose precedes the reason of the exceedingly differing opinions and assertions of several authors about the height of several very high hills. 8. Whether this inflection of the air will not very much alter the supposed distances of the planets which seems to have a very great dependence upon the hypothetical refraction or inflection of the air, and that refraction upon the hypothetical height and density of the air. For sense as I hope I have here shown the air to be quite otherwise than has been hitherto supposed, by manifesting it to be both of a vast, at least an uncertain height, and of an unconstant and irregular density, it must necessarily follow that its inflection must be varied accordingly. And therefore we may hence learn upon what sure grounds all the astronomers hitherto have built, who have calculated the distance of the planets from their horizontal parallax, for sense the refraction and parallax are so nearly allied that the one cannot be known without the other, especially by any ways that have been yet attempted, how uncertain must the parallax be when the refraction is unknown, and how easy is it for astronomers to assign what distance they please to the planets and defend them when they have such a curious subterfuge as that of refraction, wherein a very little variation will allow them liberty enough to place the celestial bodies at what distance they please. If therefore we would come to any certainty in this point we must go other ways to work. And as I have here examined the height and refractive property of the air by other ways than are usual, so must we find the parallax of the planets by ways not yet practiced and to this end I cannot imagine any better way than the observations of them by two persons at very distant parts of the earth. That lie, as near as may be, under the same meridian or degree of longitude, but differing as much in latitude as there can be places conveniently found. These two persons at certain appointed time should as near as could be, both at the same time, observe the way of the moon, Mars, Venus, Jupiter and Saturn amongst the fixed stars with a good large telescope and making little econosmes, or pictures of the small fixed stars that appear to each of them to lie in or near the way of the center of the planet, and the exact measure of the apparent diameter from the comparing of such observations together, we might certainly know the true distance or parallax of the planet, and having any one true parallax of these planets we might very easily have the other by their apparent diameters, which the telescope likewise affords us very accurately, and hence their motions might be much better known and their theories more exactly regulated. And for this purpose I know not any one place more convenient for such an observation to be made in than in the island of St. Helena upon the coast of Africa, which lies about sixteen degrees to the southwards of the line, and is very near according to the latest geographical maps in the same meridian with London. For though they may not perhaps lie exactly in the same, yet their observations being ordered accordingly to what I shall anon show, it will not be difficult to find the true distance of the planet, but where they both under the same meridian it would be much better. And because observations may be much easier and more accurately made with good telescopes than with any other instruments, it will not, I suppose, seem impertinent to explain a little what ways I judge most fit inconvenient for that particular. Such, therefore, shall be the observators for this purpose should be furnished with the best telescopes that can be had, the longer the better and more exact will their observations be, though they are somewhat the more difficultly managed. These should be fitted with a reet, or divided scale placed at such a distance within the eyeglass that they may be distinctly seen, which should be the measures of minutes and seconds. By this instrument each observator should at certain prefix times observe the moon or other planet in or very near the meridian, and because it may be very difficult to find two convenient stations that will happen to be just under the same meridian, they shall each of them observe the way of the planet both for an hour before and an hour after it arrive at the meridian, and by a line or stroke amongst the small fixed stars they shall denote out the way that each of them observe the center of the planet to be moved in for those two hours. These observations each of them shall repeat for many days together that both it may happen, that both of them may sometimes make their observations together, and that from diverse experiments we may be the better assured of what certainty and exactness such kinds of observations are like to prove. And because many of the stars which may happen to come within the compass of such an iconism or map, may be such as are only visible through a good telescope whose positions perhaps have not been noted, nor their longitudes or latitudes anywhere remarked. Therefore each observator should endeavor to insert some fixed star whose longitude and latitude is known, or with this telescope he shall find the position of some notable telescopical star inserted in his map to some known fixed star whose place in the zodiac is well-defined. Having by this means found the true distance of the moon and having observed well the apparent diameter of it at the time with a good telescope, it is easy enough by one single observation of the apparent diameter of the moon with a good glass to determine her distances in any other part of her orbit or dragon. And consequently some few observations will tell us whether she be moved in an ellipsis, which by the way may also be found even now, though I think we are yet ignorant of her true distance, and next, which without such observations I think we shall not be sure of, we may know exactly the bigness of that ellipsis or circle, and her true velocity in each part and thereby be much the better enabled to find out the true cause of all her motions. And though even now also we may by such observations in one station as here at London observe the apparent diameter and motion of the moon in her dragon, and consequently be enabled to make a better guess at the species or kind of curve in which she is moved, that is whether it be spherical or elliptical or neither, and with what proportional velocity she is carried in that curve, yet till her true parallax be known we cannot determine either. Next, for the true distance of the sun, the best way will be by accurate observations made in both these aforementioned stations of some convenient eclipse of the sun, many of which may so happen as to be seen by both. For the penumbra of the moon may, if she be sixty semi-diameters distant from the earth, and the sun above seven thousand, extend to about seventy degrees on the earth, and consequently be seen by observers as far distant as London and St. Helena, which are not full sixty-nine degrees distant. And this would much more accurately than any way that has yet been used to determine the parallax and distance of the sun. For as for the horizontal parallax I have already shown it sufficiently uncertain, nor is the way of finding it by the eclipse of the moon any other than hypothetical, and that by the difference of the true and apparent quadrature of the moon is not less uncertain, witness their deductions from it who have made use of it, for Vindaline puts that difference to be but four minutes thirty seconds, whence he deduces a vast distance of the sun, as I have before shown. Ricciola makes it a full thirty minutes, but Rhinoldist and Kircher no less than three degrees, and no wonder for if we examine the theory we shall find it so complicated with uncertainties. First, from the irregular surface of the moon and from several parallaxes that unless the dichotomy happened in the non- egesimus of the ecliptic, and that in the meridian, etc., all which happen so very seldom, that it is almost impossible to make them otherwise than uncertainly. Besides we are not yet certain, but that there may be somewhat about the moon analogous to the air about the earth, which may cause a refraction of the light of the sun and consequently make a great difference in the apparent dichotomy of the moon. Their way indeed is very rational and ingenious, and such is as much to be preferred before the way by the horizontal parallax could all the uncertainties be removed and were the true distances of the moon known. But because we find by the experiments of Vindaline, Rhinoldist, etc., that observations of this kind are very uncertain also, it were to be wished that such kind of observations made at two very distant stations were promoted. And it is so much the more desirable because from what I have now shown of the nature of the air it is evident that the refraction may be very much greater than all the astronomers hitherto have imagined it, and consequently that the distance of the moon and other planets may be much less than what they have hitherto made it. For first this inflection, I have here propounded, will allow the shadow of the earth to be much shorter than it can be made by the other hypothesis of refraction, and consequently the moon will not suffer an eclipse unless it comes very much nearer the earth than the astronomers hitherto have supposed it. Secondly, there will not in this hypothesis be any other shadow of the earth such as Kepler supposes and calls the penumbra which is the shadow of the refracting atmosphere, for the bending of the rays being altogether caused by inflection as I have already shown, all that part which is ascribed by Kepler and others after him to the penumbra or dark part, which is without the umbra tera, does clear vanish, for in this hypothesis there is no refracting surface of the air and consequently there can be no shadows such as appear in the ninth figure of the thirty-seven scheme where let ABCD represent the earth and EFGH the atmosphere which according to Kepler supposition is like a sphere of water terminated with an exact surface EFGH. Let the lines MF, LB, ID, KH represent the rays of the sun, to as manifest that all the rays between LB and ID will be reflected by the surface of the earth, BAD, and consequently the conical space BOD would be dark and obscure. But say the followers of Kepler the rays between MF and LB and between ID and KH falling on the atmosphere are refracted both at their ingress and egress out of the atmosphere nearer towards the access of the spherical shadow CO and consequently enlighten a great part of that former dark cone and shorten and contract its top to end. And because of this reflection of these rays they say there is super-induced another shell of a dark cone FPH whose apex P is yet further distant from the earth. By this penumbra say the moon is eclipsed, for it always passes between the lines 1, 2, and 3, 4. To which I say that if the air be such, as I have newly shown it to be and consequently cause such an inflection of the rays that fall into it, those dark penumbra's FYZQ, HXVT, and ORPS will all vanish, for if we suppose the air indefinitely extended, and to be nowhere bounded with a determinant refracting surface as I have shown it incapable of having from the nature of it, it will follow that the moon will nowhere be totally obscured, but when it is below the apex N of the dark blunt cone of the earth's shadow. Now from the supposition that the sun is distant about 7000 diameters, the point N, according to calculation, being not above 25 terrestrial semi-diameters from the descender of the earth, it follows that when so ever the moon eclipsed is totally darkened without affording any kind of light, it must be within 25 semi-diameters of the earth and consequently much lower than any astronomers have hitherto put it. This will seem much more consonant to the rest of the secondary planets. For the highest of Jupiter's moons is between 20 and 30 Jovial semi-diameters distant from the center of Jupiter, and the moons of Saturn much about the same number of Saturnial semi-diameters from the center of that planet. But these are but conjectures also and must be determined by such kind of observations as I have newly mentioned. Nor will it be difficult by this hypothesis to sav all the appearance of eclipses of the moon, for in this hypothesis also there will be on each side of the shadow of the earth a penumbra, not caused by the refraction of the air as in the hypothesis of Kepler, but by the faint in-lighting of it by the sun. For if in the sixth figure we suppose ESQ and GSR to be the rays that terminate the shadow from either side of the earth, ESQ coming from the upper limb of the sun and GSR from the under, it will follow that the shadow of the earth within those rays, that is the cone GSE, will be totally dark. But the sun being not a point but a large area of light there will be a secondary dark cone of shadow EPG, which will be caused by the earth's hindering part of the rays of the sun from falling on the part's GPR, and EPQ, of which have shadow or penumbra that part will appear brightest which lies nearest the terminating rays GP and EP, and those darker that lie nearest to GS and ES. When therefore the moon appears quite dark in the middle of the eclipse, she must be below S, that is between S and F, when she appears lighter near the middle of the eclipse, she must pass somewhere between RQ and S, and when she is alike light through the whole eclipse, she must pass between RQ and P. End of Section 64. Recording by Philip Gould. Section 65 of Micrographia. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Recording by Larry Wilson. Recording by Robert Hook. Observation 59 of multitudes of small stars discoverable by the telescope. Having in the last observation premised some particulars observable in the medium through which we must look upon celestial objects, I shall here add one observation of the bodies themselves. And for the specimen I have made choice of the Pleiades or seven stars, commonly so called, though in our time and climate, there appear no more than six to the naked eye. And this I did the rather because the deservedly famous Galileo, having published a picture of this asterismy, was able, it seems, with his glass to discover no more than 36, whereas with a pretty good 12-foot telescope, by which I drew this iconism, I could very plainly discover 78. Placed in the order they are ranged in the figure and of as many differing magnitudes as the asterisks, wherewith they are marked to specify there be no less than 14 several magnitudes of those stars, which are comprised within the draught, the biggest whereof is not accounted greater than one of the third magnitude. And indeed that account is much too big if it be compared with other stars of the third magnitude, especially by the help of a telescope. For them by it may be perceived that its splendor to the naked eye may be somewhat augmented by the three little stars immediately above it, which are near adjoining it. The telescope also discovers a great variety, even in the bigness of those commonly reckoned of the first, second, third, fourth, fifth, and sixth magnitude, so that should they be distinguished thereby, those six magnitudes would at least afford no less than thrice that number of magnitudes, plainly enough distinguishable by their magnitude and brightness, so that a good 12-foot glass would afford us no less than 25 several magnitudes. Nor are these all but a longer glass does yet further both more nicely distinguish the magnitudes of those already noted, and also discover several other smaller magnitudes, not discernible by the 12-foot glass. Thus have I been able with a good 36-foot glass to discover many more stars in the Pleiades than there are here delineated, and those of three or four distinct magnitudes less than any of those spots of the 14th magnitude. And by the twinkling of the diverse other places of this asterismy, when the sky was very clear, I am apt to think that with longer glasses, or such as would bear a bigger aperture, there might be discovered multitudes of other small stars, yet inconspicuous. And indeed for the discovery of small stars, the bigger the aperture be, the better adapted is the glass. For though perhaps it does make the several specs more radiant and glaring, yet by that means uniting more rays very near to one point, it does make many of those radiant points conspicuous, which by putting on a less aperture, may be found to vanish. And therefore both for the discovery of the fixed star, and for the finding of the satellites of Jupiter, before it be out of the day, or twilight, I always leave the object glass as clear without any aperture as I can, and have thereby been able to discover the satellites a long while before. I was able to discern them when the smaller apertures were put on, and at other times to see multitudes of other smaller stars, which a smaller aperture makes to disappear. In that notable asterism, also of the second sword of Orion, where the ingenious Monsieur Huygens von Surikem has discovered only three little stars in a cluster, I have found with a 36 foot glass without any aperture, the breadth of the glass being about some three inches and a half, discovered five, and the twinkliness of diverse others up and down in diverse parts of that small milky cloud. So that is not likely, but that the milieu of telescopes will afford as great a variety of new discoveries in the heavens as better microscopes would among small terrestrial bodies. And both would give us infinite cause more and more to admire the omnipotence of the creator. End of section 65. Section 66 of Micrographia. This is the LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org, recording by Larry Wilson. Micrographia by Robert Hook. Observation 60 of the Moon. Having a pretty large corner of the plate for the seven stars, void for filling it up, I have added one small specimen of the appearance of the parts of the moon by describing a small spot of it, which though taken notice of, both by the excellent Hevellius and called Moons Olympus, though I think somewhat improperly, being rather a veil, and represented by figure 10 of the 38 Scheme and also by the learned Ritualis, who calls it Hipparchus, and describes it by the figure Y. Yet how far short both of them come to the truth may be somewhat perceived by the draft, which I have here added of it in figure Z, which I drew by a 30-foot glass in October 1664, just before the moon was half enlightened, but much better by the readers diligently observing it himself at a convenient time with a glass of that length and much better yet with one of the three-score foot long, for through these it appears a very spacious veil encompassed with a ridge of hills, not very high in comparison of many other in the moon, nor yet very steep. The veil itself, A. B. C. D., is much of the figure of a pair, and from several appearances of it seems to be some very fruitful place, that is to have its surface all covered over with some kinds of vegetable substances. For in all position of the light on it, it seems to give a much fainter reflection on the more barren tops of the encompassing hills, and those are much fainter than diverse other cragged, chalky or rocky mountains of the moon, so that I am not unappet to think that the veil may have vegetables analogous to our grass, shrubs, and trees, and most of these encompassing hills may be covered with so thin a vegetable coat as we may observe the hills with us to be, such as the short sheep pasture which covers the hills of Salisbury plains. Up and down in several parts of this place here described, as there are multitudes and other places all over the surface of the moon, may be perceived several kinds of pits which are shaped almost like a dish, some bigger, some less, some shallower, some deeper, that is they seem to be a hollow hemisphere encompassed with a round rising bank, as if the substance in the middle had been digged up and thrown on either side. These seem to me to have been the effects of some motions within the body of the moon, analogous to our earthquakes. By the eruption of which, as it has thrown up a brim, a ridge round about, higher than the ambient surface of the moon, so has it left a hole, or depression in the middle proportionably lower. Diverse places resembling some of these I have observed here in England on the tops of some hills which might have been caused by some earthquake in the younger days of the world. But that which does most incline me to this belief is first the generality and diversity of the magnitude of these pits all over the body of the moon. Next, the two experimental ways by which I have made a representation of them. The first was with a very soft and well tempered mixture of tobacco pipe, clay and water, into which if I let fall any heavy body as a bullet, it would throw up the mixture round the place which for a while would make a representation not unlike these of the moon. But considering the state and condition of the moon, there seems not any probability to imagine that it should proceed from any cause analogous to this. For it would be difficult to imagine whence those bodies should come. And next, how the substance of the moons should be so soft. But if a bubble be blown under the surface of it and suffered to rise and break, or if a bullet or other body sunk into it, be pulled out from it, these departing bodies leave an impression on the surface of the mixture exactly like these of the moon, save that those also quickly subside and vanish. But the second and most notable representation was that I observed in a pot of boiling alabaster, for there that potter being by the eruption of vapors reduced to a kind of fluid consistency. If whilst it boils, it be greatly removed besides the fire, the alabaster presently ceasing to boil, the whole surface, especially that where some of the last bubbles have risen, will appear all over covered with small pits, exactly shaped like these of the moon. And by holding a lighted candle in a large dark room in diverse places to this surface, you may exactly represent all the phenomena of these pits in the moon, according as they are more or less enlightened by the sun. And that there may have been in the moon some such motion as this, which may have made these pits, will seem the more probable if we suppose it like our earth, for the earthquakes here with us seem to proceed from some such cause as the boiling of the pot of alabaster. There seeming to be generated in the earth from some subterraneous fires or heat great quantities of vapors, that is of expanded aerial substances which not presently finding a passage through the ambient parts of the earth, do as they are increased by the supplying and generating principles, and thereby having not sufficient room to expand themselves, extremely condensed at last over power with their elastic properties, the resistance of the encompassing earth, and lifting it up or cleaving it, and so shattering the parts of the earth above it, do at length where they find the parts of the earth above them more loose, make their way upwards and carrying a great part of the earth before them, not only raise a small brim around the place out of which they break, but for the most part considerable high hills and mountains, and when they break from under the sea, diverse times mountainous islands. This seems confirmed by the Vulcans in several places of the earth, the mouths of which for the most part are encompassed with a hill of a considerable height, and the tops of those hills or mountains are usually shaped very much like these pits or dishes of the moon. In instances of these we have in the descriptions of Etna in Sicily, of Hecla in Iceland, of Tenerife in the Canaries, and of several Vulcans in New Spain, described by Gage, and more especially in the eruption of late years in one of the Canary Islands, in all of which there is not probably only a considerable high hill raised about the mouth of the Vulcan, but like the spots of the moon, the top of those hills are like a dish or basin, and indeed, if one attentively considers the nature of the thing, one may find sufficient reason to judge that it cannot be otherwise. For these eruptions, whether of fire or smoke, always raising great quantities of earth before them must necessarily by the fall of those parts on either side raise very considerable heaps. Now both from the figures of them and from several other circumstances, these pits in the moon seem to have been generated much after the same manner that the holes in alabaster and the Vulcans of the earth are made. For first, it is not improbable, but that the substance of the moon may be very much like that of our earth. That is, may consist of an earthy, sandy, or rocky substance in several of its superficial parts, which parts being agitated, undermined, or heaved up by eruptions of vapors may naturally be thrown into the same kind of figured holes as the small dust or powder of alabaster. Next, it is not improbable, but that there may be generated within the body of the moon diverse such kinds of internal fires and heats as may produce such exhalations. For since we can plainly enough discover with a telescope that there are multitudes of such kind of eruptions in the body of the sun itself, which is accounted the most noble ethereal body, certainly we need not be much scandalized at such kind of alterations or corruptions in the body of this lower and less considerable part of the universe, the moon, which is only secondary or attendant on the bigger and more considerable body of the earth. Thirdly, it is not unlikely, but that supposing such a sandy or molding substance to be there found, and supposing also a possibility of the generation of the internal elastical body, whether you will call it air or vapors, it is not unlikely, I say, but that there is in the moon a principle of gravitation such as in the earth. And to make this probable, I think we need no better argument than the roundness or globular figure of the body of the moon itself, which we may perceive very plainly by the telescope to be baiting the small inequality of the hills and veils in it, which we are all of them likewise shaped or leveled as it were to answer to the center of the moon's body, perfectly of a spherical figure. That is, all the parts of it are so ranged, baiting the comparatively small ruggedness of the hills and veils, that the outmost bounds of them are equally distant from the center of the moon. And consequently, it is exceedingly probable also that they are equidistant from the center of gravitation. And indeed the figure of the superficial parts of the moon are so exactly shaped according as they should be, supposing it had a gravitating principle as the earth has, that even the figure of those parts themselves is of sufficient efficiency to make the gravitation and the other two suppositions probable, so that the other suppositions may be rather proved by this considerable circumstance or observation. Then this supposed explication can by that, for he that shall attentively observe with an excellent telescope how all the circumstances, notable in the shape of the superficial parts are, as it were, exactly adapted to suit with such a principle. Will, if he well considers the usual method of nature in its other proceedings, find abundant argument to believe it to have really there also such a principle. For I could never observe among all the mountainous or prominent parts of the moon, whereof there is a huge variety, that any one part of it was placed in such a manner that if there should be a gravitating or attracting principle in the body of the moon, it would make that part to fall or be moved out of its visible posture. Next, the shape and position of the parts is such that they shall all seem put into those very shapes they are in by a gravitating power. For first, there are but a very few cliffs or very deep declivities in the ascent of these mountains. For besides those mountains, which are by Hevelius called the Apennine Mountains and some other which seem to border on the seas of the moon and those only upon one side, as is common also in those hills that are here on the earth, there are very few that seem to have very steep ascent, but for the most part they are made very round and much resemble the make of the hills and mountains also of the earth. This may be partly perceived by the hills encompassing this veil, which I have here described, and as on the earth also, the middle most of these hills seems the highest. So is it obvious also through a good telescope and those of the moon? The veils also in many are much shaped like those of the earth. And I am apt to think that could we look upon the earth from the moon with a good telescope, we might easily enough perceive its surface to be very much like that of the moon. Now whereas in this small draft, as there would be in multitudes if the whole moon were drawn after this manner, there are several little ebullitions or dishes even in the veils themselves and in the encompassing hills also. This will from this supposition, which I have I think upon very good reason taken, be exceedingly easily explicable, for as I have several times also observed in the surface of alabaster so ordered as I had before described, so many the later eruptions of vapors be even in the middle or on the edges of the former. And other succeeding these also in time may be in the middle or edges of these, et cetera, of which there are instances enough in diverse parts of the body of the moon and by a boiling pot of alabaster will be sufficiently exemplified. To conclude therefore, it being very probable that the moon has a principle of gravitation, it affords an excellent distinguishing instance in the search after the cause of gravitation or attraction, to hint that it does not depend upon the diurnal or a terminated motion of the earth as some have somewhat inconsideratively supposed and affirmed it to do. Where if the moon has an attractive principle, whereby it is not only shaped round but does firmly contain and hold all parts united, though many of them seem as loose as the sand on the earth and that the moon is not moved about its center, then certainly the termination cannot be the cause of the attraction of the earth and therefore some other principle must be thought of, that will agree with all the secondary as well as primary planets. But this I confess is but a probability and not a demonstration, which from any observation yet made, it seems hardly capable of though how successful future endeavors promoted by the ameliorating of glasses and observing particular circumstances may be in this or any other kind must be with patients expected. End of section 66. End of micrographia by Robert Hoof.