As the full significance of the experiments shown by these extracts may not be apparent to a lay reader, it may be stated by way of premise that, ordinarily, a current only follows a closed circuit. An electric bell or electric light is a familiar instance of this rule. There is in each case an open (wire) circuit which is closed by pressing the b.u.t.ton or turning the switch, thus making a complete and uninterrupted path in which the current may travel and do its work. Until the time of Edison"s investigations of 1875, now under consideration, electricity had never been known to manifest itself except through a closed circuit. But, as the reader will see from the following excerpts, Edison discovered a hitherto unknown phenomenon--namely, that under certain conditions the rule would be reversed and electricity would pa.s.s through s.p.a.ce and through matter entirely unconnected with its point of origin. In other words, he had found the forerunner of wireless telegraphy. Had he then realized the full import of his discovery, all he needed was to increase the strength of the waves and to provide a very sensitive detector, like the coherer, in order to have antic.i.p.ated the princ.i.p.al developments that came many years afterward. With these explanatory observations, we will now turn to the excerpts referred to, which are as follows:
"November 22, 1875. New Force.--In experimenting with a vibrator magnet consisting of a bar of Stubb"s steel fastened at one end and made to vibrate by means of a magnet, we noticed a spark coming from the cores of the magnet. This we have noticed often in relays, in stock-printers, when there were a little iron filings between the armature and core, and more often in our new electric pen, and we have always come to the conclusion that it was caused by strong induction. But when we noticed it on this vibrator it seemed so strong that it struck us forcibly there might be something more than induction. We now found that if we touched any metallic part of the vibrator or magnet we got the spark. The larger the body of iron touched to the vibrator the larger the spark. We now connected a wire to X, the end of the vibrating rod, and we found we could get a spark from it by touching a piece of iron to it, and one of the most curious phenomena is that if you turn the wire around on itself and let the point of the wire touch any other portion of itself you get a spark. By connecting X to the gas-pipe we drew sparks from the gas-pipes in any part of the room by drawing an iron wire over the bra.s.s jet of the c.o.c.k. This is simply wonderful, and a good proof that the cause of the spark is a TRUE UNKNOWN FORCE."
"November 23, 1815. New Force.--The following very curious result was obtained with it. The vibrator shown in Fig. 1 and battery were placed on insulated stands; and a wire connected to X (tried both copper and iron) carried over to the stove about twenty feet distant. When the end of the wire was rubbed on the stove it gave out splendid sparks. When permanently connected to the stove, sparks could be drawn from the stove by a piece of wire held in the hand. The point X of vibrator was now connected to the gas-pipe and still the sparks could be drawn from the stove."
"Put a coil of wire over the end of rod X and pa.s.sed the ends of spool through galvanometer without affecting it in any way. Tried a 6-ohm spool add a 200-ohm. We now tried all the metals, touching each one in turn to the point X." [Here follows a list of metals and the character of spark obtained with each.]
"By increasing the battery from eight to twelve cells we get a spark when the vibrating magnet is shunted with 3 ohms. Cannot taste the least shock at B, yet between carbon points the spark is very vivid. As will be seen, X has no connection with anything. With a gla.s.s rod four feet long, well rubbed with a piece of silk over a hot stove, with a piece of battery carbon secured to one end, we received vivid sparks into the carbon when the other end was held in the hand with the handkerchief, yet the galvanometer, chemical paper, the sense of shock in the tongue, and a gold-leaf electroscope which would diverge at two feet from a half-inch spark plate-gla.s.s machine were not affected in the least by it.
"A piece of coal held to the wire showed faint sparks.
"We had a box made thus: whereby two points could be brought together within a dark box provided with an eyepiece. The points were iron, and we found the sparks were very irregular. After testing some time two lead-pencils found more regular and very much more vivid. We then subst.i.tuted the graphite points instead of iron." [26]
[Footnote 26: The dark box had micrometer screws for delicate adjustment of the carbon points, and was thereafter largely used in this series of investigations for better study of the spark. When Mr. Edison"s experiments were repeated by Mr. Batchelor, who represented him at the Paris Exposition of 1881, the dark box was employed for a similar purpose.]
After recording a considerable number of other experiments, the laboratory notes go on to state:
"November 30, 1875. Etheric Force.--We found the addition of battery to the Stubb"s wire vibrator greatly increased the volume of spark. Several persons could obtain sparks from the gas-pipes at once, each spark being equal in volume and brilliancy to the spark drawn by a single person....
Edison now grasped the (gas) pipe, and with the other hand holding a piece of metal, he touched several other metallic substances, obtained sparks, showing that the force pa.s.sed through his body."
"December 3, 1875. Etheric Force.--Charley Edison hung to the gas-pipe with feet above the floor, and with a knife got a spark from the pipe he was hanging on. We now took the wire from the vibrator in one hand and stood on a block of paraffin eighteen inches square and six inches thick; holding a knife in the other hand, we drew sparks from the stove-pipe. We now tried the crucial test of pa.s.sing the etheric current through the sciatic nerve of a frog just killed. Previous to trying, we tested its sensibility by the current from a single Bunsen cell. We put in resistance up to 500,000 ohms, and the twitching was still perceptible. We tried the induced current from our induction coil having one cell on primary,, the spark jumping about one-fiftieth of an inch, the terminal of the secondary connected to the frog and it straightened out with violence. We arranged frog"s legs to pa.s.s etheric force through. We placed legs on an inverted beaker, and held the two ends of the wires on gla.s.s rods eight inches long. On connecting one to the sciatic nerve and the other to the fleshy part of the leg no movement could be discerned, although brilliant sparks could be obtained on the graphite points when the frog was in circuit. Doctor Beard was present when this was tried."
"December 5, 1875. Etheric Force.--Three persons grasping hands and standing upon blocks of paraffin twelve inches square and six thick drew sparks from the adjoining stove when another person touched the sounder with any piece of metal.... A galvanoscopic frog giving contractions with one cell through two water rheostats was then placed in circuit.
When the wires from the vibrator and the gas-pipe were connected, slight contractions were noted, sometimes very plain and marked, showing the apparent presence of electricity, which from the high insulation seemed improbable. Doctor Beard, who was present, inferred from the way the leg contracted that it moved on both opening and closing the circuit.
To test this we disconnected the wire between the frog and battery, and placed, instead of a vibrating sounder, a simple Morse key and a sounder taking the "etheric" from armature. The spark was now tested in dark box and found to be very strong. It was then connected to the nerves of the frog, BUT NO MOVEMENT OF ANY KIND COULD BE DETECTED UPON WORKING THE KEY, although the brilliancy and power of the spark were undiminished.
The thought then occurred to Edison that the movement of the frog was due to mechanical vibrations from the vibrator (which gives probably two hundred and fifty vibrations per second), pa.s.sing through the wires and irritating the sensitive nerves of the frog. Upon disconnecting the battery wires and holding a tuning-fork giving three hundred and twenty-six vibrations per second to the base of the sounder, the vibrations over the wire made the frog contract nearly every time....
The contraction of the frog"s legs may with considerable safety be said to be caused by these mechanical vibrations being transmitted through the conducting wires."
Edison thought that the longitudinal vibrations caused by the sounder produced a more marked effect, and proceeded to try out his theory. The very next entry in the laboratory note-book bears the same date as the above (December 5, 1875), and is ent.i.tled "Longitudinal Vibrations," and reads as follows:
"We took a long iron wire one-sixteenth of an inch in diameter and rubbed it lengthways with a piece of leather with resin on for about three feet, backward and forward. About ten feet away we applied the wire to the back of the neck and it gives a horrible sensation, showing the vibrations conducted through the wire."
The following experiment ill.u.s.trates notably the movement of the electric waves through free s.p.a.ce:
"December 26, 1875. Etheric Force.--An experiment tried to-night gives a curious result. A is a vibrator, B, C, D, E are sheets of tin-foil hung on insulating stands. The sheets are about twelve by eight inches. B and C are twenty-six inches apart, C and D forty-eight inches and D and E twenty-six inches. B is connected to the vibrator and E to point in dark box, the other point to ground. We received sparks at intervals, although insulated by such s.p.a.ce."
With the above our extracts must close, although we have given but a few of the interesting experiments tried at the time. It will be noticed, however, that these records show much progression in a little over a month. Just after the item last above extracted, the Edison shop became greatly rushed on telegraphic inventions, and not many months afterward came the removal to Menlo Park; hence the etheric-force investigations were side-tracked for other matters deemed to be more important at that time.
Doctor Beard in his previously mentioned treatise refers, on page 27, to the views of others who have repeated Edison"s experiments and observed the phenomena, and in a foot-note says:
"Professor Houston, of Philadelphia, among others, has repeated some of these physical experiments, has adopted in full and after but a partial study of the subject, the hypothesis of rapidly reversed electricity as suggested in my letter to the Tribune of December 8th, and further claims priority of discovery, because he observed the spark of this when experimenting with a Ruhmkorff coil four years ago. To this claim, if it be seriously entertained, the obvious reply is that thousands of persons, probably, had seen this spark before it was DISCOVERED by Mr.
Edison; it had been seen by Professor Nipher, who supposed, and still supposes, it is the spark of the extra current; it has been seen by my friend, Prof. J. E. Smith, who a.s.sumed, as he tells me, without examination, that it was inductive electricity breaking through bad insulation; it had been seen, as has been stated, by Mr. Edison many times before he thought it worthy of study, it was undoubtedly seen by Professor Houston, who, like so many others, failed to even suspect its meaning and thus missed an important discovery. The honor of a scientific discovery belongs, not to him who first sees a thing, but to him who first sees it with expert eyes; not to him even who drops an original suggestion, but to him who first makes, that suggestion fruitful of results. If to see with the eyes a phenomenon is to discover the law of which that phenomenon is a part, then every schoolboy who, before the time of Newton, ever saw an apple fall, was a discoverer of the law of gravitation...."
Edison took out only one patent on long-distance telegraphy without wires. While the principle involved therein (induction) was not precisely a.n.a.logous to the above, or to the present system of wireless telegraphy, it was a step forward in the progress of the art. The application was filed May 23, 1885, at the time he was working on induction telegraphy (two years before the publication of the work of Hertz), but the patent (No. 465,971) was not issued until December 29, 1891. In 1903 it was purchased from him by the Marconi Wireless Telegraph Company. Edison has always had a great admiration for Marconi and his work, and a warm friendship exists between the two men. During the formative period of the Marconi Company attempts were made to influence Edison to sell this patent to an opposing concern, but his regard for Marconi and belief in the fundamental nature of his work were so strong that he refused flatly, because in the hands of an enemy the patent might be used inimically to Marconi"s interests.
Edison"s ideas, as expressed in the specifications of this patent, show very clearly the close a.n.a.logy of his system to that now in vogue.
As they were filed in the Patent Office several years before the possibility of wireless telegraphy was suspected, it will undoubtedly be of interest to give the following extract therefrom:
"I have discovered that if sufficient elevation be obtained to overcome the curvature of the earth"s surface and to reduce to the minimum the earth"s absorption, electric telegraphing or signalling between distant points can be carried on by induction without the use of wires connecting such distant points. This discovery is especially applicable to telegraphing across bodies of water, thus avoiding the use of submarine cables, or for communicating between vessels at sea, or between vessels at sea and points on land, but it is also applicable to electric communication between distant points on land, it being necessary, however, on land (with the exception of communication over open prairie) to increase the elevation in order to reduce to the minimum the induction-absorbing effect of houses, trees, and elevations in the land itself. At sea from an elevation of one hundred feet I can communicate electrically a great distance, and since this elevation or one sufficiently high can be had by utilizing the masts of ships, signals can be sent and received between ships separated a considerable distance, and by repeating the signals from ship to ship communication can be established between points at any distance apart or across the largest seas and even oceans. The collision of ships in fogs can be prevented by this character of signalling, by the use of which, also, the safety of a ship in approaching a dangerous coast in foggy weather can be a.s.sured. In communicating between points on land, poles of great height can be used, or captive balloons. At these elevated points, whether upon the masts of ships, upon poles or balloons, condensing surfaces of metal or other conductor of electricity are located. Each condensing surface is connected with earth by an electrical conducting wire. On land this earth connection would be one of usual character in telegraphy. At sea the wire would run to one or more metal plates on the bottom of the vessel, where the earth connection would be made with the water. The high-resistance secondary circuit of an induction coil is located in circuit between the condensing surface and the ground. The primary circuit of the induction coil includes a battery and a device for transmitting signals, which may be a revolving circuit-breaker operated continually by a motor of any suitable kind, either electrical or mechanical, and a key normally short-circuiting the circuit-breaker or secondary coil. For receiving signals I locate in said circuit between the condensing surface and the ground a diaphragm sounder, which is preferably one of my electromotograph telephone receivers. The key normally short-circuiting the revolving circuit-breaker, no impulses are produced in the induction coil until the key is depressed, when a large number of impulses are produced in the primary, and by means of the secondary corresponding impulses or variations in tension are produced at the elevated condensing surface, producing thereat electrostatic impulses. These electrostatic impulses are transmitted inductively to the elevated condensing surface at the distant point, and are made audible by the electromotograph connected in the ground circuit with such distant condensing surface."
The accompanying ill.u.s.trations are reduced facsimiles of the drawings attached to the above patent, No. 465,971.
V. THE ELECTROMOTOGRAPH
IN solving a problem that at the time was thought to be insurmountable, and in the adaptability of its principles to the successful overcoming of apparently insuperable difficulties subsequently arising in other lines of work, this invention is one of the most remarkable of the many that Edison has made in his long career as an inventor.
The object primarily sought to be accomplished was the repeating of telegraphic signals from a distance without the aid of a galvanometer or an electromagnetic relay, to overcome the claims of the Page patent referred to in the preceding narrative. This object was achieved in the device described in Edison"s basic patent No. 158,787, issued January 19, 1875, by the subst.i.tution of friction and anti-friction for the presence and absence of magnetism in a regulation relay.
It may be observed, parenthetically, for the benefit of the lay reader, that in telegraphy the device known as the relay is a receiving instrument containing an electromagnet adapted to respond to the weak line-current. Its armature moves in accordance with electrical impulses, or signals, transmitted from a distance, and, in so responding, operates mechanically to alternately close and open a separate local circuit in which there is a sounder and a powerful battery. When used for true relaying purposes the signals received from a distance are in turn repeated over the next section of the line, the powerful local battery furnishing current for this purpose. As this causes a loud repet.i.tion of the original signals, it will be seen that relaying is an economic method of extending a telegraph circuit beyond the natural limits of its battery power.
At the time of Edison"s invention, as related in Chapter IX of the preceding narrative, there existed no other known method than the one just described for the repet.i.tion of transmitted signals, thus limiting the application of telegraphy to the pleasure of those who might own any patent controlling the relay, except on simple circuits where a single battery was sufficient. Edison"s previous discovery of differential friction of surfaces through electrochemical decomposition was now adapted by him to produce motion at the end of a circuit without the intervention of an electromagnet. In other words, he invented a telegraph instrument having a vibrator controlled by electrochemical decomposition, to take the place of a vibrating armature operated by an electromagnet, and thus opened an entirely new and unsuspected avenue in the art.
Edison"s electromotograph comprised an ingeniously arranged apparatus in which two surfaces, normally in contact with each other, were caused to alternately adhere by friction or slip by reason of electrochemical decomposition. One of these surfaces consisted of a small drum or cylinder of chalk, which was kept in a moistened condition with a suitable chemical solution, and adapted to revolve continuously by clockwork. The other surface consisted of a small pad which rested with frictional pressure on the periphery of the drum. This pad was carried on the end of a vibrating arm whose lateral movement was limited between two adjustable points. Normally, the frictional pressure between the drum and pad would carry the latter with the former as it revolved, but if the friction were removed a spring on the end of the vibrator arm would draw it back to its starting-place.
In practice, the chalk drum was electrically connected with one pole of an incoming telegraph circuit, and the vibrating arm and pad with the other pole. When the drum rotated, the friction of the pad carried the vibrating arm forward, but an electrical impulse coming over the line would decompose the chemical solution with which the drum was moistened, causing an effect similar to lubrication, and thus allowing the pad to slip backward freely in response to the pull of its retractile spring.
The frictional movements of the pad with the drum were comparatively long or short, and corresponded with the length of the impulses sent in over the line. Thus, the transmission of Morse dots and dashes by the distant operator resulted in movements of corresponding length by the frictional pad and vibrating arm.
This brings us to the gist of the ingenious way in which Edison subst.i.tuted the action of electrochemical decomposition for that of the electromagnet to operate a relay. The actual relaying was accomplished through the medium of two contacts making connection with the local or relay circuit. One of these contacts was fixed, while the other was carried by the vibrating arm; and, as the latter made its forward and backward movements, these contacts were alternately brought together or separated, thus throwing in and out of circuit the battery and sounder in the local circuit and causing a repet.i.tion of the incoming signals.
The other side of the local circuit was permanently connected to an insulated block on the vibrator. This device not only worked with great rapidity, but was extremely sensitive, and would respond to currents too weak to affect the most delicate electromagnetic relay. It should be stated that Edison did not confine himself to the working of the electromotograph by the slipping of surfaces through the action of incoming current, but by varying the character of the surfaces in contact the frictional effect might be intensified by the electrical current. In such a case the movements would be the reverse of those above indicated, but the end sought--namely, the relaying of messages--would be attained with the same certainty.