 Chapter 5 of the Story of Electricity, this LibriVox recording is in the public domain, Recording by Ruth Golding. The Story of Electricity by John Monroe. Chapter 5 Electrolysis Having seen how electricity can be generated and stored in considerable quantity, let us now turn to its practical uses. Of these, by far the most important, are based on its property of developing light and heat as in the electric spark, chemical action as in the voltameter, and magnetism as in the electromagnet. The words current, pressure, and so on point to a certain analogy between electricity and water, which helps the imagination to figure what can neither be seen nor handled, so it must not be traced too far. Water, for example, runs by the force of gravity from a place of higher to a place of lower level. The pressure of the stream is greater, the more the difference of level or head of water. The strengths of the current or quantity of water flowing per second is greater the higher the pressure, and the less the resistance of its channel. The power of the water or its rate of doing mechanical work is greater the higher the pressure and the stronger the current. So too electricity flows by the electromotive force from a place of higher to a place of lower electric level or potential. The electric pressure is greater the more the difference of potential or electromotive force. The strengths of the electric current or quantity of electricity flowing per second is greater the higher the pressure or electromotive force and the less the resistance of the circuit. The power of the electricity or its rate of doing work is greater the higher the electromotive force and the stronger the current. It follows that a small quantity of water or electricity at a high pressure will give us the same amount of energy as a large quantity at a low pressure and our choice of one or the other will depend on the purpose we have in view. As a rule however a large current at a comparatively low or moderate pressure is found the more convenient in practice. The electricity of friction belongs to the former category and the electricity of chemistry heat and magnetism to the latter. The spark of a factional or influence machine can be compared to a highland cataract of lofty height but small volume which is more picturesque than useful and the current from a voltaic battery a thermopile or a dynamo to a lowland river which can be dammed to turn a mill. It is the difference between a skittish gelding and a tame cart horse. Not the spark from an induction coil or lyden jar but a strong and steady current at a low pressure is adapted for electrolysis or electro deposition and hence the voltaic battery or a special form of dynamo is usually employed in this work. A flash of lightning is the very symbol of terrific power and yet according to the illustrious Faraday it contains a smaller amount of electricity than the feeble current required to decompose a single drop of rain. In our simile of the mill dam and the battery or dynamo the dam corresponds to the positive pole and the river or sea below the mill to the negative pole. The mill race will stand for the wire joining the poles that is to say the external circuit and the mill wheel for the work to be done in the circuit whether it be a chemical for decomposition, a telegraph instrument, an electric lamp or any other appliance. As the current in the race depends on the head of water or difference of level between the dam and the sea as well as on the resistance of the channel, so the current in the circuit depends on the electromotive force or difference of potential between the positive and negative poles as well as on the resistance of the circuit. The relation between these is expressed by the well-known law of ohm which runs a current of electricity is directly proportional to the electromotive force and inversely proportional to the resistance of the circuit. In practice electricity is measured by various units or standards named after celebrated electricians, thus the unit of quantity is the coulomb, the unit of current or quantity flowing per second is the ampere, the unit of electromotive force is the volt, and the unit of resistance is the ohm. The quantity of water or any other electrolyte decomposed by electricity is proportional to the strength of the current. One ampere decomposes 0.00009324 gram of water per second, liberating 0.000010384 gram of hydrogen and 0.00008286 gram of oxygen. The quantity in grams of any other chemical element or ion which is liberated from an electrolyte or body capable of electrochemical decomposition in a second by a current of one ampere is given by what is called the electrochemical equivalent of the ion. This is found by multiplying its ordinary chemical equivalent or combining weight by 0.000010384, which is the electrochemical equivalent of hydrogen, thus the weight of metal deposited from a solution of any of its salts by a current of so many amperes in so many seconds is equal to the number of amperes multiplied by the number of seconds and by the electrochemical equivalent of the metal. The deposition of a metal from a solution of its salt is very easily shown in the case of copper. In fact, we have already seen that in the danial cell the current decomposes a solution of sulfate of copper and deposits the pure metal on the copper plate. If we simply make a solution of blue vitriol in a glass beaker and dip the wires from a voltaic cell into it, we shall find the wire from the negative pole become freshly coated with particles of new copper. The sulfate has been broken up and the liberated metal, being positive, gathers on the negative electrode. Moreover, if we examine the positive electrode we shall find it slightly eaten away because the sulfuric acid set free from the sulfate has combined with the particles of that wire to make new sulfate. Thus the copper is deposited on one electrode, namely the cathode, by which the current leaves the bath, and at the expense of the other electrode, that is to say the anode, by which the current enters the bath. The fact that the weight of metal deposited in this way from its salts is proportional to the current, has been utilised for measuring the strength of currents with a fine degree of accuracy. If for example the tubes of the voltammeter described on page 38 were graduated, the volume of gas evolved would be a measure of the current. Usually, however, it is the weight of silver or copper deposited from their salts in a certain time, which gives the current in amperes. Electroplating is the principal application of this chemical process. In 1805 Broneatelli took a silver medal and coated it with gold by making it the cathode in a solution of a salt of gold, and using a plate of gold for the anode. The shocks of our jewellers are now bright with teapots, salt-sellers, spoons and other articles of the table, made of inferior metals, but beautified and preserved from rust in this way. Figure 44 illustrates an electroplating bath in which a number of spoons are being plated. A portion of the vat V is cut away to show the interior, which contains a solution S of the double cyanide of gold and potassium when gold is to be laid, and the double cyanide of silver and potassium when silver is to be deposited. The electrodes are hung from metal rods, the anode A being a plate of gold or silver G, as the case may be, and the cathode C, the spoons in question. When the current of the battery or dynamo passes through the bath from the anode to the cathode, gold or silver is deposited on the spoons, and the bath recuperates its strength by consuming the gold or silver plate. Enormous quantities of copper are now deposited in a similar way, sulfate of copper being the solution and a copper plate the anode. Large articles of iron, such as the parts of ordnance, are sometimes copper-plated to preserve them from the action of the atmosphere. Seamless copper pipes for conveying steam and wires of pure copper for conducting electricity are also deposited, and it is not unlikely that the kettle of the future will be made by electrolysis. Nickel plating is another extensive branch of the industry, the white nickel forming a cloak for metals more subject to corrosion. Nickel is found to deposit best from a solution of the double sulfate of nickel and ammonia. Aluminium, however, has not yet been successfully deposited by electricity. In 1836 De La Rue observed that copper laid in this manner on another surface took on its underside an accurate impression of that surface, even to the scratches on it. And three years later, Jacobi of St. Petersburg and Jordan of London applied the method to making copies or replicas of metals and woodcuts. Even non-metallic surfaces could be reproduced in copper by taking a cast of them in wax and lining the mould with fine plum bago, which, being a conductor, served as a cathode to receive the layer of metal. It is by the process of electro-typing, or galvano plastics, that the copper faces for printing woodcuts are prepared, and copies made of seals or metals. Natural objects, such as flowers, ferns, leaves, feathers, insects and lizards, can be prettily coated with bronze or copper, not to speak of gold and silver, by a similar process. They are too delicate to be coated with black lead in order to receive the skin of metal, but they can be dipped in solutions leaving a film which can be reduced to gold or silver. For instance, they may be soaked in an alcoholic solution of nitrate of silver, made by shaking two parts of the crystals in one hundred parts of alcohol in a stoppered bottle. When dry, the object should be suspended under a glass shade, and exposed to a stream of sulphuretted hydrogen gas. Or, it may be immersed in a solution of one part of phosphorus in fifteen parts of bisulfide of carbon, one part of beeswax, one part of spirits of turpentine, one part of asphaltum, and one eighth part of cow chuck dissolved in bisulfide of carbon. This leaves a superficial film which is metallized by dipping in a solution of twenty grains of nitrate of silver to a pint of water. On this metallic film a thicker layer of gold and silver in different shades can be deposited by the current, and the silver surface may also be oxidized by washing it in a weak solution of platinum chloride. Electrolysis is also used, to some extent, in reducing metals from their ores, in bleaching fibre, in manufacturing hydrogen and oxygen from water, and in the chemical treatment of sewage. End of Chapter 5 Chapter 6 of The Story of Electricity This LibriVox recording is in the public domain, recording by Ruth Golding. The Story of Electricity by John Monroe Chapter 6 The Telegraph and Telephone Like the philosopher's stone, the elixir of youths, and perpetual motion, the telegraph was long a dream of the imagination. In the sixteenth century, if not before, it was believed that two magnetic needles could be made sympathetic, so that when one was moved the other would likewise move, however far apart they were, and thus enable two distant friends to communicate their minds to one another. The idea was prophetic, although the means of giving effect to it were mistaken. It became practicable, however, when erstid discovered that a magnetic needle could be swung to one side or the other by an electric current passing near it. The illustrious Laplace was the first to suggest a telegraph on this principle. A wire connecting the two poles of a battery is traversed, as we know, by an electric current, which makes the round of the circuit, and only flows when that circuit is complete. However long the wire may be, however far it may run between the poles, the current will follow all its windings, and finish its course from pole to pole of the battery. You may lead the wire across the ocean and back, or round the world, if you will, and the current will travel through it. The moment you break the wire or circuit, however, the current will stop. By its electromotive force it can overcome the resistance of the many miles of conductor, but unless it be unusually strong it cannot leap across even a minute gap of air, which is one of the best insulators. If then we have a simple device easily manipulated by which we can interrupt the circuit of the battery in accordance with a given code, we shall be able to send a series of currents through the wire and make sensible signals wherever we choose. These signs can be produced by the deviation of a magnetic needle, as Laplace pointed out, or by causing an electromagnet to attract soft iron, or by chemical decomposition, or any other sensible effect of the current. Ompair developed the idea of Laplace into a definite plan, and in 1830 or thereabout, Ritchie in London and Baron Schilling in St. Petersburg exhibited experimental models. In 1833 and afterwards, Professors Gauss and Weber installed a private telegraph between the observatory and the physical cabinet of the University of Göttingen. Moreover, in 1836 William Fothergild Cook, a retired surgeon of the Madras Army, attending lectures on anatomy at the University of Heidelberg, saw an experimental telegraph of Professor Monke, which turned all his thought to the subject. On returning to London he made the acquaintance of Professor Wheatstone of King's College, who was also experimenting in this direction, and in 1836 they took out a patent for a needle telegraph. It was tried successfully between the Euston Terminus and the Camden Town station of the London and Northwestern Railway, on the evening of July 25, 1837, in presence of Mr. Robert Stevenson and other eminent engineers. Wheatstone, sitting in a small room near the booking office at Euston, sent the first message to Cook at Camden Town, who at once replied, Never, said Wheatstone, did I feel such a tumultuous sensation before, as when, all alone in the still room, I heard the needle's click, and as I spelled the words, I felt all the magnitude of the invention pronounced to be practicable, without cavill or dispute. The importance of the telegraph in working railways was manifest, and yet the directors of the company were so per-blind as to order the removal of the apparatus, and it was not until two years later that the great Western Railway Company adopted it on their line, from Paddington to West Drayton, and subsequently to Slough. This was the first telegraph for public use, not merely in England, but the world. The charge for a message was only a chilling, nevertheless few persons availed themselves of the new invention, and it was not until its fame was spread abroad by the clever capture of a murderer named Towell, that it began to prosper. Towell had killed a woman at Slough, and on leaving his victim took the train for Paddington. The police, apprised of the murder, telegraphed a description of him to London. The original five-needle instrument, now in the Museum of the Post Office, had a dial in the shape of a diamond, on which were marked the letters of the alphabet, and each letter of a word was pointed out by the movements of a pair of needles. The dial had no letter Q, and as the man was described as a Quaker, the word was sent K-W-A-K-E-R. When the train arrived at Paddington, he was shadowed by detectives, and to his utter astonishment was quietly arrested in a tavern near Cannon Street. In Cook and Wheatstone's early telegraph the wire travelled the whole round of the circuit, but it was soon found that a return wire in the circuit was unnecessary, since the earth itself could take the place of it. One wire from the sending station to the receiving station was sufficient, provided the apparatus at each end were properly connected to the ground. This use of the earth not only saved the expense of a return wire, but diminished the resistance of the circuit, because the earth offered practically no resistance. Figure 45 is a diagram of the connections in a simple telegraph circuit. At each of the stations there is a battery B-B-1, an interrupter or sending key K-K-1 to make and break the continuity of the circuit. A receiving instrument R-R-1 to indicate the signal currents by their sensible effects, and connections with ground or earth plates E-E-1 to engage the earth as a return wire. These are usually copper plates buried in the moist subsoil or the water pipes of a city. The line wire is commonly of iron supported on poles, but insulated from them by earthenware cups or insulators. At the station on the left the key is in the act of sending a message, and at the post on the right it is conformably in the position for receiving the message. The key is so constructed that when it is at rest it puts the line in connection with the earth through the receiving instrument and the earth plate. The key K consists essentially of a spring lever with two platinum contacts, so placed that when the lever is pressed down by the hand of the telegraphist it breaks contact with the receiver R and puts the line wire L in connection with the earth E through the battery B, as shown on the left. A current then flows into the line and traverses the receiver R-1 at the distant station, returning or seeming to return to the sending battery by way of the earth plate E-1 on the right and the intermediate ground. The duration of the current is at the will of the operator who works the sending key, and it is plain that signals can be made by currents of various lengths. In the morse code of signals, which is now universal, only two lengths of current are employed, namely a short momentary pulse produced by instant contact of the key and a jet given by a contact about three times longer. These two signals are called dot and dash, and the code is merely a suitable combination of them to signify the several letters of the alphabet. Thus E, the communist letter in English, is telegraphed by a single dot and the letter T by a single dash, while the letter A is indicated by a dot followed after a brief interval or space by a dash. Obviously if two kinds of current are used, that is to say, if the poles of the battery are reversed by the sending key and the direction of the current is subsequently reversed in the circuit, there is no need to alter the lengths of the signal currents, because a momentary current sent in one direction will stand for a dot and in the other direction for a dash. As a matter of fact, the code is used in both ways, according to the nature of the line and receiving instrument. On submarine cables and with needle and mirror instruments, the signals are made by reversing currents of equal duration, but on landlines worked by morse instruments and sounders they are produced by short and long currents. The morse code is also used in the army for signalling by waving flags or flashing lights, and may also be serviceable in private life. Telegraph clerks have been known to speak with each other in company by linking the right and left eye or tapping their teaspoon on a cup and saucer. Any two distinct signs, however made, can be employed as a telegraph by means of the morse code, which runs as shown in Figure 46. Readers note the morse code for some letters and numbers appears to be incomplete in this transcription and also differs from other editions of the same book. End of Readers note. a dot dash b dash dot dot dot c dot dot dot d dash dot dot e dot f dot dash dot g dash dash dot h dot space dot dot i dot dot j dash dot dash dot k dash dot dash l dash dash m dash space dash n dash dot o dot space dot q dot dot dash dot r dot space dot dot s dot dot dot t dash u dot dot dash v dot dot dot dash w dot dash x dot dash dot dot y dot dot space dot dot z dot dot dot space dot and dot space dot dot period dot dot dash dash dot dot comma dot dash dot dash one dot dash dash dot two dot dot dash dot dot three dot dot dot dash dot four dot dot dot dot dash five dash dash dash six dot dot dot dot dot seven dash dash dot dot eight dash dot dot space dot dot nine dash dot dot dash zero dash dash dash the international morse code used elsewhere is the same as the above with the following exceptions c dash dot dash dot f dot space dash dot j dot dash dash dash l dot dash dot dot o dash dash dash p dot dash dash dot q dash dash dot dash r dot dash dot x dash dot dot dash y dash dot dash dash z dash dash dot dot the receiving instruments r r1 may consist of a magnetic needle pivoted on its center and surrounded by a coil of wire through which the current passes and deflects the needle to one side or the other according to the direction in which it flows such was the pioneer instrument of cook and wheatstone which is still employed in england in a simplified form as the single and double needle instrument on some of the local lines and in railway telegraphs the signals are made by sending momentary currents in opposite directions by a double current key which unlike the key k in figure 45 reverses the poles of the battery in putting the line to one or the other and thus making the dot signal with the positive and the dash signal with the negative pole it follows that if the dot is indicated by a throw of the needle to the right side a dash will be given by a throw to the left most of the telegraph instruments for landlines are based on the principle of the electromagnet we have already seen page 59 how on pair found that a spiral of wire with a current flowing in it behaved like a magnet and was able to suck a piece of soft iron into it if the iron is allowed to remain there as a core the combination of coil and core becomes an electromagnet that is to say a magnet which is only a magnet so long as the current passes figure 47 represents a simple horseshoe electromagnet as invented by sturgeon a u-shaped core of soft iron is wound with insulated wire w and when a current is sent through the wire the core is found to become magnetic with a north pole in one end and a south pole in the other these poles are therefore able to attract a separate piece of soft iron or armature a when the current is stopped however the core ceases to be a magnet and the armature drops away in practice the electromagnet usually takes the form shown in figure 48 where the poles are two bobbins or solenoids of wire b and a is the armature such an electromagnet is a more powerful device than a swinging needle and better able to actuate a mechanism it became the foundation of the recording instrument of samuel morse the father of the telegraph in america the morse or rather morse and veil instrument actually marks the signals in dots and dashes on a ribbon of moving paper figure 49 represents the morse instrument in which an electromagnet m attracts an iron armature a when a current passes through its bobbins and by means of a lever l connected with the armature raises the edge of a small disc out of an ink pot i against the surface of a traveling slip of paper p and marks a dot or dash upon it as the case may be the rest of the apparatus consists of details and accessories for its action and adjustment together with the sending key k which is used in asking for repetitions of the words if necessary a permanent record of the message is of course convenient nevertheless the operators prefer to read the signals by the ear rather than the eye and to the annoyance of morse would listen to the click of the marking disc rather than decipher the marks on the paper consequently alfred veil the collaborator of morse who really invented the morse code produced a modification of the recording instrument working solely for the ear the sounder as it is called has largely driven the printer from the field this neat little instrument is shown in figure 50 where m is the electromagnet and a is the armature which chatters up and down between two metal stops as the current is made and broken by the sending key and the operator listening to the sounds interprets the message letter by letter and word by word the motion of the armature in both of these instruments takes a sensible time but alexander bane of thurso by trade a watchmaker and by nature a genius invented a chemical telegraph which was capable of a prodigious activity the instrument of bane resembled the morse in marking the signals on a tape of moving paper but this was done by electrolysis or electrochemical decomposition the paper was soaked in a solution of iodide of potassium in starch and water and the signal currents were passed through it by a marking stylus or pencil of iron the electricity decomposed the solution in its passage and left a blue stain on the paper which corresponded to the dot and dash of the morse apparatus the bane telegraph can record over a thousand words a minute as against 40 to 50 by the morse or sounder nevertheless it has fallen into disuse perhaps because the solution was troublesome it is stated that a certain blind operator could read the signals by the smell of the chemical action and we can well believe it in fact the telegraph appeals to every sense for a deaf clock can feel the movements of a sounder and the signals of the current can be told without any instrument by the mere taste of the wires inserted in the mouth a skillful telegraphist can transmit 25 words a minute with the single current key and nearly twice as many by the double current key and if we remember that an average English word requires 15 separate signals the number will seem remarkable but by means of Wheatstone's automatic sender a hundred and fifty words or more can be sent in a minute among telegraphs designed to print the message in roman type that of professor david edward Hughes is doubtless the fittest since it is now in general use on the continent and conveys our continental news in this apparatus the electromagnet on attracting its armature presses the paper against a revolving type wheel and receives the print of a type so that the message can be read by a novice to this effect the type wheel at the receiving station has to keep in perfect time as it revolves so that the right letter shall be above the paper when the current passes small varieties of the type printer are employed for the distribution of news and prices in most of the large towns being located in hotels restaurants saloons and other public places and reporting prices of stocks and bonds horse races and sporting and general news the duplex system whereby two messages one in either direction can be sent over one wires simultaneously without interfering and the quadruplex system whereby four messages two in either direction are also sent at once have come into use where the traffic over the lines is very great both of these systems and their modifications depend on an ingenious arrangement of the apparatus at each end of the line by which the signal currents sent out from one station do not influence the receivers there but leave them free to indicate the currents from the distant station when the wheat stone automatic sender is employed with these systems about 500 words per minute can be sent through the line press news is generally sent by night and it is on record that during a great debate in parliament as many as half a million words poured out of the central telegraph station at st martinsburg grand in a single night to all parts of the country errors occur now and then through bad penmanship or the similarity of certain signals and amusing telegrams have been sent out as when the nomination of mr brand for the speakership of the commons took the form of proposed to brand speaker and an excursion party assured their friends at home of their security by the message arrived all tight telegraphs in the literal sense of the word which actually write the message as with a pen and make a copy or facsimile of the original have been invented from time to time such are the telegraphic pen of mr e a cooper and the telegraphs of mr j h robertson and mr elisha gray the first two are based on a method of varying the strength of the current in accordance with the curves of the handwriting and making the varied current actuate by means of magnetism a writing pen or stylus at the distant station the instrument of gray which is the most successful works by intermittent currents or electrical impulses that excite electromagnets and move the stylus at the far end of the line they are too complicated for description here and are not of much practical importance telegraphs for transmitting sketches and drawings have also been devised by dablancourt and others but they have not come into general use of late another step forward has been taken by mr amstutz who has invented an apparatus for transmitting photographic pictures to a distance by means of electricity the system may be described as a combination of the photograph and telegraph an ordinary negative picture is taken and then impressed on a gelatin plate sensitized with bichromate of potash the parts of the gelatin in light become insoluble while the parts in shade can be washed away by water in this way a relief or engraving of the picture is obtained on the gelatin and a cross section through the plate would if looked at edgeways appears serrated or up and down like a section of country or the trace of the stylus in the record of a phonograph the gelatin plate thus carved by the action of light and water is wrapped around a revolving drum or barrel and a spring stylus or point is caused to pass over it as the barrel revolves after the manner of a phonographic cylinder in doing so the stylus rises and falls over the projections in the plate and works a lever against a set of telegraph keys which open electric contacts and break the connections of an electric battery which is joined between the keys and the earth there are four keys and when they are untouched the current splits up through four by paths or bobbins of wire before it enters the line wire and passes to the distant station when any of the keys are touched however the corresponding by path or bobbin is cut out of circuit the suppression of a by path or channel for the current has the effect of adding to the resistance of the line and therefore of diminishing the strength of the current when all the keys are untouched the resistance is least and the current strongest on the other hand when all the keys but the last are touched the resistance is greatest and the current weakest by this device it is easy to see that as the stylus or tracer sinks into a hollow of the gelatin or rises over a height the current in the line becomes stronger or weaker at the distant station the current passes through a solenoid or hollow coil of wire connected to the earth and magnetizes it so as to pull the soft iron plug or core with greater or less force into its hollow interior the up and down movement of the plug actuates a graving stylus or point through a lever and engraves a copy of the original gelatin trace on the surface of a wax or gelatin plate overlying another barrel or drum which revolves at a rate corresponding to that of the barrel at the transmitting station in this way a facsimile of the gelatin picture is produced at the distant station and an electrotype or cliche of it can be made for printing purposes the method is in fact a species of electric line graving and mr amstutz hopes to apply it to engraving on gold silver or any soft metal not necessarily at a distance we know that an electric current in one wire can induce a transient current in a neighboring wire and the fact has been utilized in the united states by felps and others to send messages from moving trains the signal currents are intermittent and when they are passed through a conductor on the train they excite corresponding currents in a wire run along the track which can be interpreted by the hum they make in a telephone experiments recently made by mr wh priests for the post office show that with currents of sufficient strength and proper apparatus messages can be sent through the air for five miles or more by this method of induction we come now to the submarine telegraph which differs in many respects from the overland telegraph obviously since water and moist earth is a conductor a wire to convey an electric current must be insulated if it is intended to lie at the bottom of the sea or buried underground the best materials for the purpose yet discovered are gutter percha and india rubber which are both flexible and very good insulators the first submarine cable was laid across the channel from dover to calle in 1851 and consisted of a copper strand coated with gutter percha and protected from injury by an outer sheath of hemp and iron wire it is the general type of all the submarine cables which have been deposited since then in every part of the world as a rule the armor or sheathing is made heavier for sure water than it is for the deep sea but the electrical portion or core that is to say the insulated conductor is the same throughout the first atlantic cable was laid in 1858 by syris w field and a company of british capitalists but it broke down and it was not until 1866 that a new and successful cable was laid to replace it figure 51 represents various cross sections of an atlantic cable deposited in 1894 the inner star of 12 copper wires is the conductor and the black circle around it is the gutter percha or insulator which keeps the electricity from escaping into the water the core in shallow water is protected from the bites of turritos by a brass tape and the envelope or armor consists of hemp and iron wire preserved from corrosion by a covering of tape and a compound of mineral pitch and sand the circuit of a submarine line is essentially the same as that of a landline except that the earth connection is usually the iron sheathing of the cable in lieu of an earth plate on a cable however at least a long cable the instruments for sending and receiving the messages are different from those employed on a landline a cable is virtually a lidon jar or condenser and the signal currents in the wire induce opposite currents in the water or earth as these charges hold each other the signals are retarded in their progress and altered from sharp sudden jets to lagging undulations or waves which tend to run together or coalesce the result is that the separate signal currents which enter a long cable issue from it at the other end in one continuous current with pulsations at every signal that is to say in a lapsing stream like a jet of water flowing from a constricted spout the receiving instrument must be sufficiently delicate to manifest every pulsation of the current its indicator in fact must respond to every rise and fall of the current as a float rides on the ripples of a stream such an instrument is the beautiful mirror galvanometer of lord kelvin x president of the royal society which we illustrate in figure 52 where c is a coil of wire with a small magnetic needle suspended in its heart and d is a steel magnet supported over it the needle m figure 53 is made of watch spring cemented to the back of a tiny mirror the size of a half dime which is hung by a single fiber of floss silk inside an air cell or chamber with a glass lens g in front and the coil c surrounds it array of light from a lamp l figure 52 falls on the mirror and is reflected back to a scale s on which it makes a bright spot now when the coil c is connected between the end of the cable and the earth the signal current passing through it causes the tiny magnet to swing from side to side and the mirror moving with it throws the beam up and down the scale the operator sitting by watches the spot of light as it flips and flickers like a firefly in the darkness and spells out the mysterious message a condenser joined in the circuit between the cable and the receiver or between the receiver and the earth has the effect of sharpening the waves of the current and consequently off the signals the double current key which reverses the poles of the battery and allows the signal currents to be of one length that is to say all dots is employed to send the message another receiving instrument employed on most of the longer cables is the siphon recorder of lord kelvin shown in figure 54 which marks or writes the message on a slip of traveling paper essentially it is the inverse of the mirror instrument and consists of a light coil of wire s suspended in the field between the poles of a strong magnet m the coil is attached to a fine siphon p filled with ink and sometimes kept in vibration by an induction coil so as to shake the ink in fine drops upon a slip of moving paper the coil is connected between the cable and the earth and as the signal current passes through it swings to one side or the other pulling the siphon with it the ink therefore marks a wavy line on the paper which is in fact a delineation of the rise and fall of the signal current and a record of the message the dots in this case are represented by the waves above and the dashes by the waves below the middle line as may be seen in the following alphabet which is a copy of one actually written by the recorder on a long submarine cable owing to induction the speed of signaling on long cables is much slower than on landlines of the same length and only reaches from twenty five to forty five words a minute on the Atlantic cables or thirty to fifty words with an automatic sending key but this rate is practically doubled by employing the murehead duplex system of sending two messages one from each end at the same time the relation of the telegraph to the telephone is analogous to that of the lower animals and man in a telegraph circuit with its clicking key at one end and its chattering sound at the other we have in fact an apish forerunner of the exquisite telephone with its mysterious microphone and oracular plate nevertheless the telephone descended from the telegraph in a very indirect manner if at all and certainly not through the sounder the first practical suggestion of an electric telephone was made by monsieur Charles Borceux a french telegraphist in 1854 but to all appearance nothing came of it in 1860 however Philippe Reyes a german schoolmaster constructed a rudimentary telephone by which music and a few spoken words were sent finally in 1876 Mr Alexander Graham Bell a scottman residing in canada and subsequently in the united states exhibited a capable speaking telephone of his invention at the centennial exhibition philadelphia figure 56 represents an outside view and section of the bell telephone as it is now made where m is a bar magnet having a small bobbin or coil of fine insulated wire c girdling one pole in front of this coil there is a circular plate of soft iron capable of vibrating like a diaphragm or the drum of the ear a cover shaped like a mouthpiece oh fixes the diaphragm all round and the wires w w serve to connect the coil in the circuit the soft iron diaphragm is of course magnetized by the induction of the pole and would be attracted bodily to the pole were it not fixed by the rim so that only its middle is free to move now when a person speaks into the mouthpiece the sonorous waves impinge on the diaphragm and make it vibrate in sympathy with them being magnetic the movement of the diaphragm to and from the bobbin excites corresponding waves of electricity in the coil after the famous experiment of faraday page 64 if this undulatory current is passed through the coil of a similar telephone at the far end of the line it will by reverse action set the diaphragm in vibration and reproduce the original sonorous waves the result is that when another person listens at the mouthpiece of the receiving telephone he will hear a faithful imitation of the original speech the bell telephone is virtually a small magneto-electric generator of electricity and when two are joined in circuit we have a system for the transmission of energy as the voice is the motive power its torque though distinct is comparatively feeble and further improvements were made before the telephone became as serviceable as it is now edison in 1877 was the first to invent a working telephone which instead of generating the current merely controlled the strengths of it as the sluice of a mill dam regulates the flow of water in the lead du morcelle had observed that powder of carbon altered in electrical resistance under pressure and edison found that lamp black was so sensitive as to change in resistance under the impact of the sonorous waves his transmitter consisted of a button or wafer of lamp black behind a diaphragm and connected in the circuit on speaking to the diaphragm the sonorous waves pressed it against the button and so varied the strength of the current in a sympathetic manner the receiver of edison was equally ingenious and consisted of a cylinder of prepared chalk kept in rotation and a brass stylus rubbing on it when the undulatory current passed from the stylus to the chalk the stylus slipped on the surface and being connected to a diaphragm made it vibrate and repeat the original sounds this electromotograph receiver was however given up and a combination of the edison transmitter and the bell receiver came into use at the end of 1877 professor D. E. Hughes a distinguished Welshman inventor of the printing telegraph discovered that any loose contact between two conductors had the property of transmitting sounds by varying the strengths of an electric current passing through it two pieces of metal for instance two nails or ends of wire when brought into a loose or crazy contact under a slight pressure and traversed by a current will transmit speech two pieces of hard carbon are still better than metals and if properly adjusted will make the tread of a fly quite audible in a telephone connected with them such is the famous microphone by which a faint sound can be magnified to the ear figure 57 represents what is known as the pencil microphone in which M is a pointed rod of hard carbon delicately poised between two brackets of carbon which are connected in circuit with a battery B and a bell telephone T the joints of rod and bracket are so sensitive that the current flowing across them is affected in strengths by the slightest vibration even the walking of an insect if therefore we speak near this microphone the sonorous waves causing the pencil to vibrate will so vary the current in accordance with them as to reproduce the sounds of the voice in the telephone the true nature of the microphone is not yet known but it is evident that the air or ether between the surfaces in contact plays an important part in varying the resistance and therefore the current in fact a small voltaic arc not luminous but dark seems to be formed between the points and the vibrations probably alter its length and consequently its resistance the fact that a microphone is reversible and can act as a receiver though a poor one tends to confirm this theory moreover it is not unlikely that the slipping of the stylus in the electromotograph is due to a similar cause be this as it may there can be no doubt that carbon powder and the lamp black of the eddison button are essentially a cluster of microphones many varieties of the Hughes microphone under different names are now employed as transmitters in connection with the bell telephone figure 58 represents a simple micro telephone circuit where m is the Hughes microphone transmitter t the bell telephone receiver b the battery and ee the earth plates but sometimes the return wire is used in place of the earth the line wire is usually of copper and its alloys which are more suitable than iron especially for long distances just as the signal currents in the submarine cable induce corresponding currents in the seawater which retard them so the currents in a land wire induce corresponding currents in the earth but in aerial lines the earth is generally so far away that the consequent retardation is negligible except in fast working on long lines the bell telephone however is extremely sensitive and this induction affects it so much that a conversation through one wire can be overheard on a neighbouring wire moreover there is such a thing as self induction in a wire that is to say a current in a wire tends to induce an opposite current in the same wire which is practically equivalent to an increase of resistance in the wire it is particularly observed at the starting and stopping of a current and gives rise to what is called the extra spark seen in breaking the circuit of an induction coil it is also active in the vibratory currents of the telephone and like ordinary induction tends to retard their passage copper being less susceptible of self induction than iron is preferred for trunk lines the disturbing effect of ordinary induction is avoided by using a return wire or loop circuit and crossing the going and coming wires so as to make them exchange places at intervals moreover it is found that an induction coil in the telephone circuit like a condenser in the cable circuit improves the working and hence it is usual to join the battery and transmitter with the primary wire and the secondary wire with the line and the receiver the longest telephone line as yet made is that from new york to chicago a distance of nine hundred and fifty miles it is made of thick copper wire erected on cedar poles thirty five feet above the ground induction is so strong on submarine cables of fifty or a hundred miles in length that the delicate waves of the telephone current are smoothed away and the speech is either muffled or entirely stifled nevertheless a telephone cable twenty miles long was laid between dover and calle in 1891 and another between strand raw and donagadie more recently thus placing great britain on speaking terms with france and other parts of the continent figure 59 shows a form of telephone apparatus employed in the united kingdom in it the transmitter and receiver together with a call bell which are required at each end of the line are neatly combined the transmitter is a microphone in which the loose joint is a contact of platinum on hard carbon it is fitted up inside the box together with an induction coil and m is the mouthpiece for speaking to it the receiver is a pair of bell telephones t t which are detached from their hooks and held to the ear a call bell b serves to ring up the correspondent at the other end of the line accepting private lines the telephone is worked on the exchange system that is to say the wires running to different persons converge in a central exchange where by means of an apparatus called a switchboard they are connected together for the purpose of conversation a telephone exchange would make an excellent subject for the artist he delights to paint us a row of venetian bead stringers or a band of civilian cigarette makers but why does he shirk a bevy of industrious girls working a telephone exchange let us peep into one of these retired haunts where the modern fates are cutting and joining the lines of electric speech between man and man in a great city the scene is a long handsome room or gallery with a singular piece of furniture in the shape of an l occupying the middle this is the switchboard in which the wires from the offices and homes of the subscribers are concentrated like the nerves in a ganglion it is known as the multiple switchboard an american invention and is divided into sections over which the operators preside the lines of all the subscribers are brought to each section so that the operator can cross connect any two lines in the whole system without leaving her chair each section of the board is in fact an epitome of the whole but it is physically impossible for a single operator to make all the connections of a large exchange and the work is distributed amongst them a multiplicity of wires is therefore needed to connect say two thousand subscribers these are all concealed however at the back of the board and in charge of the electricians the young lady operators have nothing to do with these and so much the better for them as it would puzzle their minds a good deal worse than a ravelled skein of thread their duty is to sit in front of the board in comfortable seats at a long table and make the needful connections the call signal of a subscriber is given by the drop of a disk bearing his number the operator then asks the subscriber by telephone what he wants and on hearing the number of the other subscriber he wishes to speak with she takes up a pair of brass plugs coupled by a flexible conductor and joins the lines of the subscribers on the switchboard by simply thrusting the plugs into holes corresponding to the wires the subscribers are then free to talk with each other undisturbed and the end of the conversation is signalled to the operator every instant the call discs are dropping the connecting plugs are thrust into the holes and the girls are asking hello hello are you there who are you have you finished yet all this constant activity goes on quietly deftly we might say elegantly and in comparative silence for the low tones of the girlish voices are soft and pleasing and the harsher sounds of the subscriber are unheard in the room by all save the operator who attends to him end of chapter six chapter seven of the story of electricity this LibriVox recording is in the public domain recording by Ruth Golding the story of electricity by John Munro chapter seven electric light and heat the electric spark was of course familiar to the early experimenters with electricity but the electric light as we know it was first discovered by Sir Humphrey Davy the Cornish philosopher in the year 1811 or there about with the magic of his genius Davy transformed the spark into a brilliant glow by passing it between two points of carbon instead of metal if as in figure 60 we twist the wires plus and minus which come from a voltaic battery say of 20 cells about two carbon pencils and bring their tips together in order to start the current then draw them a little apart we shall produce an artificial or mimic star a sheet of dazzling light which is called the electric arc is seen to bridge the gap it is not a true flame for there is little combustion but rather a nebulous blaze of silvery luster in a bluish veil of heated air the points of carbon are white hot and the positive is eaten away into a hollow or crater by the current which violently tears its particles from their seat and whirls them into the fierce vortex of the arc the negative remains pointed but it is also worn away about half as fast as the positive this wasting of the carbons tends to widen the arc too much and break the current hence in arc lamps meant to yield the light for hours the sticks are made of a good length and a self-acting mechanism feeds them forward to the arc as they are slowly consumed thus maintaining the splendor of the illumination many ingenious lamps have been devised by serra du bosque semen's rocky and others some regulating the arc by clockwork and electromagnetism or by thermal and other effects of the current they are chiefly used for lighting halls and railway stations streets and open spaces search lights and lighthouses they are sometimes naked but as a rule their brightness is tempered by globes of ground or opal glass in search lights a parabolic mirror projects all the rays in any one direction and in lighthouses the arc is placed in the focus of the condensing lenses and the beam is visible for at least 20 or 30 miles on clear nights very powerful arc lights equivalent to hundreds of thousands of candles can be seen for 100 or 150 miles figure 61 illustrates the pilsen lamp in which the positive carbon g runs on rollers r r through the hollow interior of two solenoids or coils of wire m m1 and carries at its middle a spindle shaped piece of soft iron c the current flows through the solenoid m on its way to the arc but a branch or shunted portion of it flows through the solenoid m1 and as both of these solenoids act as electromagnets on the soft iron c each tending to suck it into its interior the iron rests between them when their powers are balanced when however the arc grows too wide and the current therefore becomes too weak the shunt solenoid m1 gains a purchase over the main solenoid m and pulling the iron core towards it feeds the positive carbon to the arc in this way the balance of the solenoids is readjusted the current regains its normal strength the arc its proper width and the light its brilliancy figure 62 is a diagrammatic representation of the brush arc lamp x and y are the line terminals connecting the lamp in circuit on the one hand the current splits and passes around the hollow spools h h1 then to the rod n through the carbon k the arc the carbon k1 and then through the lamp frame to y on the other hand it runs in a resistance fine wire coil around the magnet t thence to y the operation of the lamp is as follows k and k1 being in contact a strong current starts through the lamp energizing h and h1 which suck in their core pieces n and s lifting c and by it the washer clutch w and the rod n and carbon k establishing the arc k is lifted until the increasing resistance of the lengthening arc weakens the current in h h1 and a balance is established as the carbons burn away c gradually lowers until a stop under w holds it horizontal and allows n to drop through w and the lamp starts anew if for any reason the resistance of the lamp becomes too great or the circuit is broken the increased current through t draws up its armature closing the contacts m thus short circuiting the lamp through a thick heavy wire coil on t which then keeps m closed and prevents the dead lamp from interfering with the others on its line numerous modifications of this lamp are in very general use davey also found that a continuous wire or stick of carbon could be made white hot by sending a sufficient current through it and this fact is the basis of the incandescent lamp now so common in our homes wires of platinum iridium and other in oxidizable metals raised to incandescence by the incandescence by the current are useful in firing mines but they are not quite suitable for yielding a light because at a very high temperature they begin to melt every solid body becomes red hot that is to say emits rays of red light at a temperature of about a thousand degrees fahrenheit yellow rays at thirteen hundred degrees blue rays at fifteen hundred degrees and white light at two thousand degrees it is found however that as the temperature of a wire is pushed beyond this figure the light emitted becomes far more brilliant than the increase of temperature would seem to warrant it therefore pays to elevate the temperature of the filament as high as possible unfortunately the most refractory metals such as platinum and alloys of platinum with iridium fuse at a temperature of about three thousand four hundred and fifty degrees fahrenheit electricians have therefore forsaken metals and fallen back on carbon for producing a light in eighteen forty five mister state devised an incandescent lamp consisting of a fine rod or stick of carbon rendered white hot by the current and to preserve the carbon from burning in the atmosphere he enclosed it in a glass bulb from which the air was exhausted by an air pump Edison and swan in eighteen seventy eight and subsequently went a step further and substituted a filament or fine thread of carbon for the rod the new lamp united the advantages of wire in point of form with those of carbon as a material the Edison filament was made by cutting thin slips of bamboo and charring them the swan by carbonizing linen fiber with sulfuric acid it was subsequently found that a hard skin could be given to the filament by flashing it that is to say heating it to incandescence by the current in an atmosphere of hydrocarbon gas the filament thus treated becomes dense and resilient figure 63 represents an ordinary glow lamp of the Edison swan type where e is the filament molded into a loop and cemented to two platinum wires or electrodes p penetrating the glass bulb l which is exhausted of air platinum is chosen because it expands and contracts with temperature about the same as glass and hence there is little chance of the glass cracking through unequal stress the vacuum in the bulb is made by a mercurial air pump of the schweingel sort and the pressure of air in it is only about one millionth of an atmosphere the bulb is fastened with a holder like that shown in figure 64 where two little hooks H connected to screw terminals t t are provided to make contact with the platinum terminals of the lamp p figure 63 and the spiral spring by pressing on the bulb ensures a good contact figure 65 is a cut of the ordinary Edison lamp and socket one end of the filament is connected to the metal screw ferrule at the base the other end is attached to the metal button in the center of the extreme bottom of the base screwing the lamp into the socket automatically connects the filament on one end to the screw on the other to an insulated plate at the bottom of the socket the resistance of such a filament hot is about 200 ohms and to produce a good light from it the battery or dynamo ought to give an electromotive force of at least 100 volts few voltaic cells or accumulators have an electromotive force of more than two volts therefore we require a battery of 50 cells joined in series each cell giving two volts and the whole set a hundred volts the strength of current in the circuit must also be taken into account to yield a good light such a lamp requires or takes about half an ampere hence the cells must be chosen with regard to their size and internal resistance as well as to their kind so that when the battery in series is connected to the lamp the resistance of the whole circuit including the filament or lamp the battery itself and the connecting wires shall give by ohms law a current of half an ampere it will be understood that the current has the same strength in every part of the circuit no matter how it is made up thus if half of an ampere is flowing in the lamp it is also flowing in the battery and wires an Edison swan lamp of this model gives the light of about 15 candles and is well adapted for illuminating the interior of houses the temperature of the carbon filament is about 3450 degrees fahrenheit that is to say the temperature at which platinum melts similar lamps of various sizes and shapes are also made some equivalent to as many as a hundred candles and fitted for large halls or streets others emitting a tiny beam like the spark of a glow worm and designed for medical examinations or lighting flowers jewels and dresses in theaters or ballrooms the electric incandescent lamp is pure and healthy since it neither burns nor pollutes the air it is also cool and safe for it produces little heat and cannot ignite any inflammable stuffs near it hence its peculiar merit is a light for colliers working in fiery mines independent of air it acts equally well under water and is therefore used by divers moreover it can be fixed wherever a wire can be run does not tarnish gilding and lends itself to the most artistic decoration electric lamps are usually connected in circuit on the series parallel and three wire system the series system is shown in figure 66 where the lamps l l follow each other in a row like beads on a string it is commonly reserved for the arc lamp which has a resistance so low that a moderate electromotive force can overcome the added resistance of the lamps but of course if the circuit breaks at any point all the lamps go out the parallel system is illustrated in figure 67 where the lamps are connected between two main conductors crosswise like the steps of a ladder the current is thus divided into cross channels like water used for irrigating fields and it is obvious that although the circuit is broken at one point say by the rupture of a filament all the lamps do not go out figure 68 exhibits the Edison three wire system in which two batteries or dynamos are connected together in series and a third or central main conductor is run from their middle poles the plan saves the return wire for if two generators had been used separately four mains would have been necessary the parallel and three wire systems in various groups with or without accumulators as local reservoirs are chiefly employed for incandescent lamps the main conductors conveying the current from the dynamos are commonly of start copper insulated with air like telegraph wires or cables coated with india rubber or gutter percha and buried underground or suspended overhead the branch and lamp conductors or leads are finer wires of copper insulated with india rubber or silk the current of an installation or section of one is made and broken at will by means of a switch or key turned by hand it is simply a series of metal contacts insulated from each other and connected to the conductors with a sliding contact connected to the dynamo which travels over them to guard against an excess of current on the lamps cutouts or safety fuses are inserted between the switch and the conductors or at other leading points in the circuit they're usually made of short slips of metal foil or wire which melt or deflagrate when the current is too strong and thus interrupt the circuit there is some prospect of the luminosity excited in a vacuum tube by the alternating currents from a dynamo or an induction coil becoming an illuminant crooks has obtained exquisitely beautiful glows by the phosphorescence of gems and other minerals in a vacuum bulb like that shown in figure 69 where a and b are the metal electrodes on the outside of the glass a heap of diamonds from various countries emit red orange yellow green and blue rays ruby sapphire and emerald give a deep red crimson or lilac phosphorescence and sulfate of zinc a magnificent green glow tesla has also shown that vacuum bulbs can be lit inside without any outside connection with the current by means of an apparatus like that shown in figure 70 where d is an alternating dynamo c a condenser p s the primary and secondary coils of a sparking transformer t t two metal sheets or plates and s b the exhausted bulbs the alternating or seesaw current in this case charges the condenser and excites the primary coil p while the induced current in the secondary coil s charges the terminal plates t t so long as the bulbs or tubes are kept within the space between the plates they are filled with a soft radiance and it is easy to see that if these plates covered the opposite walls of a room the vacuum lamps would yield a light in any part of it electric heating bids fair to become almost as important as electric illumination when the arc was first discovered it was noticed that platinum gold quartz ruby and diamond in fine the most refractory minerals were melted in it and ran like wax ores and salts of the metals were also vaporized and it was clear that a powerful engine of research had been placed in the hands of the chemist as a matter of fact the temperature of the carbons in the arc is comparable to that of the sun it measures 5000 to 10 000 degrees Fahrenheit and is the highest artificial heat known so William Siemens was among the first to make an electric furnace heated by the arc which fused and vaporized metallic ores so that the metal could be extracted from them aluminium chromium and other valuable metals are now smelted by its means and rough brilliance such as those found in diamond mines and meteoric stones have been crystallized from the fumes of carbon like whore frost in a cold mist the electric arc is also applied to the welding of wires boiler plates rails and other metal work by heating the parts to be joined and fusing them together cooking and heating by electricity are coming more and more into favour owing to their cleanliness and convenience kitchen ranges including ovens and grills entirely heated by the electric current are finding their way into the best houses and hotels most of these are based on the principle of incandescence the current heating a fine wire or other conductor of high resistance in passing through it figure 71 represents an electric kettle of this sort which requires no outside fire to boil it since the current flows through fine wires of platinum or some highly resisting metal embedded in fireproof insulating cement in its bottom figures 72 and 73 are a saucepan and a flat iron heated in the same way figure 74 is a cigar lighter for smoking rooms the fuse f consisting of short platinum wires which become red hot when it is unhooked and at the same time the lamp z is automatically lit figure 75 is an electric radiator for heating rooms and passages after the manner of stoves and hot water pipes quilts for beds warmed by fine wires inside have also been brought out a constant temperature being maintained by a simple regulator and it is not unlikely that personal clothing of the kind will soon be at the surface of invalids and chilly mortals more especially to make them comfortable on their travels an ingenious device places an electric heater inside a hot water bag thus keeping it at a uniform temperature for sick room and hospital use end of chapter seven