Electricity and Magnetism Part 6

TELEPHONY.

In the foregoing chapters I have described the method of transmitting musical tones telegraphically and its applications to multiple telegraphy, as well as to a mode of communicating with a moving railroad-train. As I stated in a former chapter, after discovering a method of transmitting harmony as well as melody, I had in mind two lines of development, one in the direction of multiple telegraphy, and the other that of the transmission of articulate speech. I will not attempt to give the names of all the people who have contributed to the development of the telephone (as this alone would fill a volume) but only describe my own share in the work--leaving history to give each one due credit for his part. While I do not intend, here, to enter into any controversy regarding the priority of the invention of the telephone, I wish to say that from the time I began my researches, in the winter of 1873-4, until some time after I had filed my specification for a speaking or articulating telephone, in the winter of 1875-76, I had no idea that any one else had done or was doing anything in this direction.

I wish to say further that if I had filed my description of a telephone as an application for a patent instead of as a caveat, and had prosecuted it to a patent, without changing a word in the specification as it stands to-day, I should have been awarded the priority of invention by the courts. I am borne out in this a.s.sertion by the highest legal authority. In law, a _caveat_ (Latin word, meaning "Let him beware") is a warning to other inventors, to protect an incomplete invention; whereas in fact the invention to be protected may be complete. An _application_ for a patent is presumed by the law to be for a completed invention; but it may be, and very often is, incomplete. It would often make a very great difference if decisions were rendered according to the facts in the case rather than according to rules of law and practice, that sometimes work great injustice to individuals.

As has been said in another chapter, in the summer of 1874 I went to Europe in the interest of the telephone, taking my apparatus, as then developed, with me. I came home early in the fall and resumed my experimental work. Many interesting as well as amusing things occurred during these experiments.

I remember that in the fall or early winter of 1874 I was in Milwaukee with my apparatus carrying on some experiments on a wire between Milwaukee and Chicago. I had my musical transmitter along, and one evening, for the entertainment of some friends at the Newhall House, a wire was stretched across the street from the telegraph office into one of the rooms of the hotel. A great number of tunes were played at the telegraph-office by Mr. Goodridge, who was my a.s.sistant at that time, which were transmitted across the street, as before stated. In those days it was a common practice in telegraphy to use one battery for a great number of lines. For instance, starting with one ground-wire which connected with, say, the negative pole of the battery, from the positive pole two, three or a half-dozen lines might be connected, running in various directions, connecting with the ground at the further end, thus completing their circuits. For use in transmitting tones across the street that evening we connected our line-wire on to the telegraph company's battery, which consisted of 100 or more cells, and which had four or five more lines radiating from the end of the battery to different parts of Wisconsin. Our line was tapped on to the battery (without changing any of its connections) twenty cells from the ground-wire. In transmitting, each vibration would momentarily shut off these twenty cells from the lines that were connected with the whole battery. The effect of this (an effect that we did not antic.i.p.ate at the time) was to send a vibratory current out on all the lines that were connected with that single battery as well as across the street. A great many familiar tunes were played during the course of an hour or two which, unconsciously for us, were creating great consternation throughout the State of Wisconsin, in many of the offices through which these various lines pa.s.sed.

Next morning reports and inquiries began to come in from various towns and cities west, northwest and north, giving details of the phenomena that were noticed on the instruments located in the various offices along the lines. They reported their relays as singing tunes; one party said he thought the instruments were holding a prayer-meeting from the fact that they seemed to be singing hymn-tunes for quite a while, but this notion was finally dissipated, because they grew hilarious and sang "Yankee Doodle."

One operator, up in the pine woods of northern Wisconsin, did not seem to take the cheerful view of it that some of the others did. He was sitting alone in the telegraph-office that evening when he thought he heard the notes of a bugle in the distance; he got up and went to the door to listen, but could hear nothing; but on coming back into the room he heard the same bugle notes very faintly. He was inclined to be somewhat superst.i.tious and grew very nervous; finally, on looking around, he located the sound in his relay, but this did not help matters with him. With superst.i.tious awe he listened to the instrument for a few moments, while it gave out the solemn tones of "Old Hundred," then it suddenly jumped into a hilarious rendering of "Yankee Doodle." This was too much for our nervous friend, and hastily putting on his overcoat, he left the office for the night.

On another occasion, when I was giving a lecture in one of the cities outside of Chicago, where exhibitions of music transmitted from Chicago were given, one of the operators along the line was very much astonished by his switchboard suddenly becoming musical. Orders had been given for the instruments in all the local offices to be cut out of the particular line that I was using. Hence the instrument in this particular office was not in the circuit through which the tunes were being transmitted.

The wire, however, ran through his switchboard, and owing probably to a loose connection, or an induced effect, there was a spark that leaped across a short s.p.a.ce at each electrical pulsation that pa.s.sed through the line, thus reproducing the notes of the various tunes played.

You will remember in one of the chapters on sound (Volume II.), it is stated that a musical tone is made up of a succession of sounds repeated at equal intervals, and that the pitch of the tone is determined by the number of sound-impulses per second. Applying this law to the sparks, you will be able to see how the switchboard played tunes for the operator.

In the foregoing experiments in transmitting musical tones telegraphically, I used a great many different varieties of receivers.

Some of them were designed with metal diaphragms mounted over single electromagnets, not unlike the receiver of an ordinary telephone. These instruments would both transmit and receive articulate speech when placed in circuit with the right amount of battery to furnish the necessary magnetism. However, they were not used in that way at the time they were first made--in 1874. These I called common receivers, as they were designed to reproduce all tones equally well. I designed and constructed another form of receiver, based somewhat upon the theory of the harmonic telegraph.

This consisted of an electromagnet of considerable size, mounted upon a wooden rod about ten feet long. Mounted upon this rod were also resonating boxes or tubes made of wood of the right size to have their air-cavities correspond with the various pitches of the transmitting-reeds, so that each tone would be re-enforced by some one of these air-cavities, thus giving a louder and more resonant effect to the musical notes.

Here were two types of receiver, one that would receive one sound as well as another, but none of them so loud, while the other was constructed on the principle of selection and re-enforcement, so that a particular note would be sounded by the box having a cavity corresponding to the pitch of the tone, and was much louder and of much better quality than I could get from the diaphragm receiver. One of these receivers pointed to the harmonic telegraph and the other to the speaking telephone. I knew that I had a receiver that would reproduce articulate speech or anything else that could be transmitted.

My first conceptions of an articulate speech-transmitter were somewhat complicated. I conceived of a funnel made of thin metal having a great number of little riders, insulated from the funnel at one end and resting lightly in contact with the funnel at the other end. These riders were to be made of all sizes and weights so as to be responsive to all rates of vibration. In the light of the present day we know that such an arrangement would have transmitted articulate speech, but perhaps not so well as a single point would do when properly adjusted.

My mind clung to this idea till in the fall of 1875, when an observation I made upon the street changed the whole course of my thinking and solved the problem. The incident I refer to took place in Milwaukee, where I was then experimenting. One day while out on an errand I noticed two boys with fruit-cans in their hands having a thread attached to the center of the bottom of each can and stretched across the street, perhaps 100 feet apart. They were talking to each other, the one holding his mouth to his can and the other his ear. At that time I had not heard of this "lovers' telegraph," although it was old. It is said to have been used in China 2000 years ago.

The two boys seemed to be conversing in a low tone with each other and my interest was immediately aroused. I took the can out of one of the boy's hands (rather rudely as I remember it now), and putting my ear to the mouth of it I could hear the voice of the boy across the street. I conversed with him a moment, then noticed how the cord was connected at the bottom of the two cans, when, suddenly, the problem of electrical speech-transmission was solved in my mind. I did not have an opportunity immediately to construct an instrument, as I had a partner who was furnishing money for the development of the harmonic telegraph and would not listen to any collateral experiments. I remember sitting down by this partner one day and telling him what I could do in the way of transmitting speech through a wire. I told him I thought it would be very valuable if worked out. He gave me a look that I shall never forget, but he did not say a word. The look conveyed more meaning than all the words he could have said, and I did not dare broach the subject again.

However, as soon as I found opportunity, without saying a word to anybody except my patent lawyer, I filed a description, accompanied by drawings, of a speaking telephone which stands in history to-day as the first complete description on record of the operation of the speaking telephone. It described an apparatus which, when constructed, worked as described, and it is a matter of history that the first articulate speech electrically transmitted in this country was by a transmitter constructed on the principle described, and almost identically after the drawings in my caveat. While the transmitter described in this caveat was not the best form, it would transmit speech, and it contained the foundation principle of all the telephone transmitters in use to-day.

There are two methods of transmitting speech. One is known as the magneto method and the other that of varying the resistance of the circuit. My first transmitter was devised on the latter principle.

I append to this extracts from my specification filed Feb. 14, 1876:

_To All Whom It May Concern:_--Be it known that I, Elisha Gray of Chicago, in the County of Cook and State of Illinois, have invented a new art of transmitting vocal sounds telegraphically, of which the following is a specification: It is the object of my invention to transmit the tones of the human voice through a telegraphic circuit, and reproduce them at the receiving-end of the line, so that actual conversations can be carried on by persons at long distances apart. I have invented and patented methods of transmitting musical impressions or sounds telegraphically, and my present invention is based upon a modification of the principle of said invention, which is set forth and described in letters patent of the United States, granted to me July 27, 1875, respectively numbered 166,095 and 166,096, and also in an application for letters patent of the United States, filed by me, Feb. 23, 1875. * * * My present belief is that the most effective method of providing an apparatus capable of responding to the various tones of the human voice is a tympanum, drum, or diaphragm, stretched across one end of the chamber, carrying an apparatus for producing fluctuations in the potential of the electric circuit and consequently varying in its power. * * * The vibrations thus imparted are transmitted through an electric circuit to the receiving-station, in which circuit is included an electromagnet of ordinary construction, acting upon a diaphragm to which is attached a piece of soft iron, and which diaphragm is stretched across a receiving vocalizing chamber _C_, somewhat similar to the corresponding vocalizing chamber _A_.

The diaphragm at the receiving-end of the line is thus thrown into vibrations corresponding with those at the transmitting-end, and audible sounds or words are produced.

The obvious practical application of my improvement will be to enable persons at a distance to converse with each other through a telegraphic circuit, just as they now do in each other's presence, or through a speaking-tube.

I claim as my invention the art of transmitting vocal sounds or conversations telegraphically through an electric circuit.

This specification was accompanied by cuts of the transmitter and receiver connected by a line-wire and showing one person talking to the transmitter and another listening at the receiver. These cuts may be seen in various books on the subject of telephony.

CHAPTER XVI.

HOW THE TELEPHONE TALKS.

Everybody knows what the telephone is because it is in almost every man's house. But while everybody knows what it is, there are very few (comparatively speaking) that know how it works. If you remember what has been said about sound and electromagnetism it will not be hard to understand.

When any one utters a spoken word the air is thrown into shivers or vibrations of a peculiar form, and every different sound has a different form. Therefore, every articulate word differs from every other word, not only as a shape in the air, but as a sensation in the brain, where the air-vibrations have been conducted through the organ of hearing; otherwise we could not distinguish between one word and another. Every different word produces a different sensation because there is a physical difference, as a shape or motion, in the air where it is uttered. If one word contains 1000 simultaneous air-motions and another 1500 you can see that there is a physical or mechanical difference in the air.

The construction of the simplest form of telephone is as follows: Take a piece of iron rod one-half or three-quarters of an inch long and one-quarter inch thick, and after putting a spool-head on each end to hold the wire in place wind it full of fine insulated copper wire; fasten the end of this spool to the end of a straight-bar permanent magnet. Then put the whole into a suitable frame, and mount a thin circular diaphragm (membrane or plate) of iron or steel, held by its edges, so that the free end of the spool will come near to but not touch the center of the diaphragm. This diaphragm must be held rigidly at the edges.

Now if the two ends of the insulated copper wires are brought out to suitable binding-screws the instrument is done.

The permanent steel magnet serves a double purpose. When the telephone was first used commercially, the instrument now used as a receiver was also used as a transmitter. As a transmitter it is a dynamo-electric machine. Every time the iron diaphragm is moved in the magnetic field of the pole of the permanent magnet, which in this case is the free end of the spool (the iron of the spool being magnetic by contact with the permanent magnet), there is a current set up in the wire wound on the spool; a short impulse, lasting only as long as the movement lasts. The intensity of the impulse will depend upon the amplitude and quickness of the movement of the diaphragm. If there is a long movement there will be a strong current and vice versa. If a sound is uttered, and even if the mult.i.tude of sounds that are required to form a word, be spoken to the diaphragm, the latter partakes in kind of the air-motions that strike it. It swings or vibrates in the air, and if it is a perfect diaphragm it moves exactly as the air does, both as to amplitude and complexity of movement. You will remember that in the chapter on sound-quality (Vol. II) it was said that there were hundreds and sometimes thousands of superposed motions in the tones of some voices that gave them the element we call quality.

All these complex motions are communicated by the air to the diaphragm, and the diaphragm sets up electric currents in the wire wound on the spool, corresponding exactly in number and form, so that the current is molded exactly as the air-waves are. Now, if we connect another telephone in the circuit, and talk to one of them, the diaphragm of the other will be vibrated by the electric current sent, and caused to move in sympathy with it and make exactly the same motions relatively, both as to number and amplitude.

It will be plain that if the receiving diaphragm is making the same motions as the transmitting diaphragm, it will put the air in the same kind of motion that the air is in at the transmitting end, and will produce the same sensation when sensed by the brain through the ear. If the air-motion is that of any spoken word it will be the same at both ends of the line, except that it will not be so intense at the receiving-end; it is the same relatively. And this is how the telephone talks.

I have said that the permanent magnet had two functions. In the case of the transmitter it is the medium through which mechanical is converted into electrical energy. It corresponds to the field-magnet of the dynamo, while the diaphragm corresponds to the revolving armature, and the voice is the steam-engine that drives it. In the second place, it puts a tension on the diaphragm and also puts the molecules of the iron core of the magnet in a state of tension or magnetic strain, and in that condition both the molecules and the diaphragm are much more sensitive to the electric impulses sent over the wire from the transmitter. This fact was experimented upon by the writer as far back as 1879 and published in the Journal of the American Electrical Society. At the present day this form of telephone is used only as a receiver.

Transmitters have been made in a variety of forms, but there are only two generic methods of transmission. One is the magneto method--the one we have described--and the other is effected by varying the resistance of a battery current. The former will work without a battery, as the voice acting on the wire around the magnet through the diaphragm creates the current; in the latter the current is created by the battery but molded by the voice. In the latter method the current pa.s.ses through carbon contacts that are moved by the diaphragm. Carbon is the best substance, because it will bear a wider separation of contact without actually breaking the current. When carbon points are separated that have an electric current pa.s.sing through them, there is an arc formed on the same principle as the electric arc-light.

Great improvements in details have been made in the telephone since its first use, but no new principles have been discovered as applied to transmission.

We have spoken in another place regarding the various claimants to the invention of the telephone, but here is one that has been overlooked. A young man from the country was in a telegraph-office at one time and was left alone while the operator went to dinner. Suddenly the sounder started up and rattled away at such a rate that the countryman thought something should be done. He leaned down close to the instrument and shouted as loudly as possible these words: "The operator has gone to dinner." From what we know now of the operation of the telephone I have no doubt but that he transmitted his voice to some extent over the wire.

This young man's claims have never been put forward before, and we are doing him tardy justice. But his claim is quite as good as many others set forth by people who think they invent, whenever it occurs to them that something new might possibly be done, if only somebody would do it.

And when that somebody does do it they lay claim to it.

In the early days of the telephone it was not supposed that a vocal message could be transmitted to a very great distance. However, as time went on and experiments were multiplied the distance to which one could converse with another through a wire kept on increasing.

In these days, as every one knows, it is a daily occurrence that business men converse with each other, telephonically, for a distance of 1000 miles or more; in fact, it is possible to transmit the voice through a single circuit about as great a distance as it is possible to practically telegraph. This leads us to speak of another telegraphic apparatus which we have not heretofore mentioned, and that is the telegraphic repeater. It is a common notion that messages are sent through a single circuit across the continent, but this is not the case, although the circuits are very much longer than they were some years ago. The repeater is an instrument that repeats a message automatically from one circuit to another. For instance, if Chicago is sending a message to New York through two circuits, the division being in Buffalo, the repeater will be located at Buffalo and under the control of both the operator at Chicago and the operator in New York.

When Chicago is sending, one part of the repeater works in unison with the Chicago key and is the key to the New York circuit, which begins at Buffalo. When New York is sending the other part of the repeater operates, which becomes a key which repeats the message to the Chicago line. In this way the practical result is the same as though the circuit were complete from New York to Chicago. At the present day some of the copper wires and perhaps some of the larger iron wires are used direct from Chicago to New York without repet.i.tion, but all messages between New York and San Francisco are automatically repeated at least twice and under certain conditions of weather oftener. I can remember that in wet weather in the old days, with such wires as they had then (being No. 9 iron with bad joints, which gave the circuit a high resistance) that these repeaters would be inserted at Toledo, Cleveland, Buffalo and Albany in order to work from Chicago to New York. Under such conditions the transmission would necessarily be slow, because an armature time will be lost at each repeater. Regarding each repeater as a key, when Chicago depresses his key the armature of the next repeater must act, and then the next successively, and all of this takes time, although only a small fraction of a second.

The repeater was a very delicate instrument and had to be handled by a skilled operator. Every wire must be in its place or the instrument would fail to operate. I remember on one occasion in Cleveland that along in the middle of the night the repeater failed to work. The operator knew nothing of the principle of its operation, so that when it failed he had to appeal to some of his superiors.

At this time there was no one in the office who knew how to adjust it, so they had to send up to the house of the superintendent and arouse him from his sleep and bring him down to the office. He looked under the table and found that one of the wires had loosened from its binding-post and was hanging down. He said immediately, "Here's the trouble; I should think you could have seen it yourself." The operator replied, "I did see that, but I didn't think one wire would make any difference." He learned the lesson that all electricians have had to learn--that even one wire makes all the difference in the world. But this operator was no worse in that respect than some of his superiors. One of the heads of the Cleveland office at one time in the early days wanted to give some directions to the office at Buffalo. He told the operator at the key to tell Buffalo so and so, when the operator replied: "I can't do it; Buffalo has his key open." The official immediately said with severity: "Tell him to close it." He forgot that it would be as difficult for him to tell him to close it, as it would have been to have sent the original message.

But let us go back to the telephone. While it is possible to send a message from New York to San Francis...o...b.. telegraph, it is not possible to telephone that distance, because as yet no one has been able to devise a repeater that will transfer spoken words from one line to another satisfactorily. But unless the printer and publisher bestir themselves some one may accomplish the feat before this little book reaches the reader. If this proves to be true, let the writer be the first to congratulate the successful inventor.

CHAPTER XVII.

SUBMARINE CABLES.

The first attempts at transmitting messages through wires laid in water were made about 1839. These early experiments were not very successful, because the art of wire-insulation had not attained any degree of perfection at that time. It was not until gutta-percha began to be used as an insulator for submarine lines that any substantial progress was made.