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by the intervals of non-conducting paper, and which continued after the discharge from the battery ceased. Mr. Edison arranged a magnet introduced into the circuit by means of a branch wire issuing from the main wire before it reached the receiver, and joining it again between the receiver and the earth. On reaching the branch wire the electric current parts into two, one portion passing along the main wire through the chemically-prepared receiving paper to the earth-the other following the branch wire. When this current, passing along the branch wire round the magnet, weakens in the least degree, an antagonistic current is generated by the magnet, part of which flows round the small circuit formed by the branch wire and portion of the main wire containing the receiver, while the remainder escapes to the earth. This antagonistic magnetic discharge neutralises the static discharge through the prepared paper. Another method of overcoming the effects of the static discharge is this: When the current induced by the battery ceases, the static electricity discharges itself at both ends of the wire. Consequently there is somewhere in the wire a neutral point where there is no flow. If the receiver is placed at this neutral point an incredible speed may be attained. By the use of a sufficient quantity of coiled line the neutral point may be obtained anywhere, e.g., at either end of the Atlantic cable. New York has in this manner been made the neutral point from Washington, and a speed of three thousand words a minute obtained.
The recording of the message was accomplished by means of the metal point ending the telegraph wire meeting a sheet of paper moistened with water. The current of electricity decomposes the water into its elements oxygen and hydrogen. If the metal point be of iron, the liberated oxygen attacks it, causing rust. If to the water wherewith the paper is moistened be added a chemical which combining with the rust gives a colouration to the paper, the automatic record is complete. If an iron point is used, the ferro-cyanide of potassium will unite with the particle of rust on the point and form Prussian blue. If a tin point, another chemical used, and another colour is produced. With this enormous increase of speed to 3000 words a minute, a more sensitive solution than any hitherto used became necessary. Mr. Edison spent many months in the search for an appropriate metal and chemical, and tested many hundred working solutions. At last he hit upon the combination of the metal tellurium with paper steeped in salt water. This union produced the most perfect success. It differed from the previous combinations in that it is the hydrogen instead of the oxygen which is the active agentforming with the tellurium a yellow compound, which quickly blackens on exposure to air. The tellurium has the additional advantage of cutting off the signals very sharply, thus aiding in overcoming the static discharge from the line. The purpose of the salt is to render the paper a better conductor, so that the water may be more rapidly decomposed.
The inventor succeeded in recording the Lord's Prayer in distinct characters in the space of an inch. To obtain a record of 3000 words a minute, each word averaging five letters, and each letter five electrical impulses, the metal and chemical must act on each other, producing a new chemical combination 45,000 times in one minute. Our speech may reach 160 words a minute. A good telegraph operator writes about forty words a minute; therefore the wire can carry as many words as twenty men can speak, talking as fast as they can, or eighty men copy in the same time. During the first year that Mr. Edison's machine was in use between New York and Washington it transmitted more than three millions of messages. Owing to litigation with rival companies, the use of it has had to be discontinued until the questions involved have been settled in the courts. During the time that the system was in practical operation the inventor was at work upon a machine which should perforate and record in the form of Roman letters, so that thus the paper might be taken direct from the wire, and delivered to the person ad. dressed. He also conceived the idea of a small perforating machine by means of which anybody might punch his message at home and send the strip to the telegraph office for transmission. The company proposed to charge so much a yard, instead of so much a word, for the transmission, leaving the sender free to crowd as much as he liked into the space.
Unfortunately, the litigation put a stop to the entire system, and for lack of funds these portions of the invention have never been perfected.
Another apparatus which Mr. Edison has perfected and patented is his quadruplex telegraph, by which four messages may be sent at the same time over the same wire. Two currents of diverse strength can be transmitted simultaneously in the same direction without interfering one with another, just as a ripple and a great wave may run on the same stream of water at the same time. Other two diverse currents may be transmitted in the opposite direction, and, unlike waves of water, they will meet and pass the first two without causing disturbance to any of the four. The quadruplex apparatus was used with excellent results by the Western Union Telegraph Company. The electric pen for multiplying copies of letters and drawings is another of Mr. Edison's patents, of which he owns one hundred and fifty. Of these about a dozen are of real importance; the others have been taken out rather as guards against possible infringements of the more valuable patents.
Among so many marvellous inventions, the most marvellous, at all events to the popular mind, are the varieties of speaking machines with which Mr. Edison's name is associated. It gives the impression of one's having strayed into a romance of Wonderland, instead of contemplating the solid science of a solid earth, when it comes to bottling up speech and setting it on a shelf, to be uncorked a century hence like good port wine, or when words can be spoken into a machine, whence they shall reissue hundreds of miles away, according as may be desired, either in a great big gruff voice like that of the huge bear in the fairy-tale, or as the middle voice of the middle-sized bear, or else as the little wee soft voice of the wee-wee bear.
At the time when Professor Bell exhibited his first telephone, Mr. Edison had in his laboratory a precisely similar apparatus which he had devised some months before, for the purpose of reproducing the vibrations of a tuning-fork. Had he chanced to sound a vocal note, or utter words into this device, he would have anticipated Professor Bell in the discovery of the magneto-telephone. As it was, Professor Bell's patent, though not interfering with Edison's right to use his own machine as a reproducing apparatus for sound, debarred him from using it for the purpose of transmitting vocal effects. He therefore set to work about the invention of a galvanic transmitter. The graduated sound-waves of the human voice as received on the diaphragm of the telephone must be represented by equally graduated waves of electric current; a series of experiments was therefore entered upon with the object of determining whether any matter or compound existed, or could be formed, which would supply by its expansion and contraction a sufficiently delicate variation of resistance to produce the desired effect of increasing and decreasing the resistance of a current. He began at one end of his stock of chemicals, and tried them all-some two thousand. He found that various forms of carbon responded the best to the vibrations produced on the diaphragm of the telephone by the human voice, but none were perfectly satisfactory. He was looking round for something else to try, when his assistant brought him the broken chimney of a kerosene lamp, encrusted with lampblack from the smoke. This he scraped off, and moulded into a button about the size of a sixpence, experimented with it, and the result was a complete solution of the problem. He had now a complete telephone, independent of that of Professor Bell, and superior to his, in that the strength of the currents is not limited by the vocal power. Thus longer lines could be worked, and a greater volume of sound obtained from the receiving instrument. The carbon telephone was patented in England in 1877. But Mr. Edison's labour was only half accomplished by the perfect carbon transmitter. He next set to work upon an electro-chemical receiver. In the series of experiments already recorded in automatic telegraphy with the metal point and chemical solution, he observed this phenomenon : When a strip of paper, steeped in a solution of certain chemicals, was subjected to the action of the electric current, its surface became smoother. As soon as the current was withdrawn, it regained its normal character. If the strip of paper were placed upon a metal base connected with one pol- of a volcanic battery, and a strip of platinum wire connected with the other pole were pressed firmly down on the paper and moved along by muscular force or clockwork; then, despite the downward pressure, the platinum strip would move along freely as long as the current continued, but if the current were interrupted, the motion of the wire would be instantly stopped by the normal friction of the moist paper. Endeavouring by additional force to overcome this friction, and at the same moment restoring the electric current, it was found that the wire would be instantly released, and would involuntarily slip over the paper as if upon ice. Here was a power to put in motion matter at a distance by means of electricity without the intervention of an electro-magnet. Mr. Edison applied this new principle to the telephone, substituting a cylinder of chalk, saturated with an alkaline solution, for the original paper, the friction of the chalk being more uniform owing to its finer particles. The cylinder is mounted on a shaft which is rotated by a hand crank. A brass strip faced with platinum, attached to the centre of a disc of mica, projects over the cylinder, and bears with considerable pressure upon the chalk by means of a spring. The electric current is made to pass from the brass strip to and through the chalk cylinder at the point of friction. When the crank is turned so as to rotate the cylinder outward from the face of the disc, the friction between the cylinder and strip drags the centre of the disc inward more or less. If now an impulse of electricity is passed over the wire, the friction is destroyed and the disc by its own tension regains its normal position. Thus the disc is drawn in one direction by the friction, in the other by its own tension; when this is united with the carbon-transmitter, we have a perfect telephone, and such power can be obtained as will cause the reproduction of the voice in greater or less volume than was given forth by the transmitter. It can either whisper a secret or roar a command. One day, while experimenting on an automatic telegraph transmitter, Mr. Edison tried tinfoil to receive the indentations of the recorder instead of paper, and was surprised to see how readily it received them. These identations, passing under another needle, were to repeat the message automatically to another wire. A few days later, the fancy seized him to fix a needle point to the diaphragm of a telephone, and try whether the vibration of the diaphragm, when spoken against, would cause the needle to prick his finger. It did so, and he wondered what would be the effect on a slip of paper. He tried the experiment, and, sure enough, there was a sort of indented tracki Then it occurred to him to try what would result from drawing this indented slip under the point again, following the working of the automatic transmitter. The effect was one which almost made him wild. A sound like a smothered cry of words seeking utterance issued from the diaphragm. He worked, oblivious of food or sleep, until he had made a grooved cylinder, and put a piece of tinfoil on it—to this be attached the diaphragm and shouted into it. On turning the crank the words were reproduced with distinct articulation and marvellous elocution, and the phonograph took its place among the wonders of the day. While pursuing experiments in electric lighting, Mr. Edison developed some striking phenomena arising from the heating of metals by flames and by the electric current. After further investigation of the phenomena, he succeeded in condensing certain metals so that they increased in density four or five times beyond what had hitherto been deemed possible. The series of experiments also referred to the volatilisation of metals in vacuo. He succeeded in obtaining with a condensed platinum wire with a radiating surface only about equal to a grain of buckwheat an electric light equal to the light of eight standard candles. The wire before being subjected to this process would scarcely give out the light of one candle. Thus he is enabled, by the increased capacity of platinum, to withstand high temperature, to employ small radiating surfaces and reduce the energy required for the light. Mr. Edison's electric light machine combines the smallest resistance with the greatest electro-motive force.
Mr. Edison has, notwithstanding his being the wizard of the day a humorous side to his character, and an imperturbable good humour, yet even he must find it difficult to be amused with the curiosity of the sight-seeing public. In 1876 he moved out to Menlo Park, some twentyfour miles from New York, where he hoped he would, at a sufficiently inconvenient distance from the city, be comparatively free from visitors. But it was no use; a gentleman asked the privilege of presenting a few friends; he arrived on the scene with a small party of one hundred and seventy-five persons !—and it is nothing uncommon for a “special train ” full of visitors from Boston to be announced. Edison may be driven yet to carry out a natural law and throw out some device for his own protection. He does allow sometimes that he will probably be tempted to “blow up somebody yet;" and he once declared that he was considering the idea of connecting a battery with his gate, so that every body who
, touched it should be straightway knocked down.
Menlo Park is a little hamlet, quiet enough in itself, a mere group of some 'half - a - dozen yellow and chocolate houses. Upon a hill Edison has built his laboratory. On the ground floor he has a machine room, where there is an engine of ten-horse power and a collection of expensive tools, so that any appliance can be made under his own eye. He has a costly scientific library; but his great possessions appear to be those which are of use to him in his work. He has thousands of bottles containing chemicals, and he makes a point of having some of every known chemical or mineral, in case he should need it.
When you go to his house he may very possibly answer your inquiry for “Mr. Edison,” himself; or, if not, you will be shown into his