In the year 1617 Strada, an Italian Jesuit, proposed to telegraph news without wires by means of two sympathetic needles made of loadstone so balanced that when one was turned the other would turn with it. Each needle was to have a dial with the letters on it. This would have been very nice if it had only worked, but it was not based on any known law of nature.
Many attempts at telegraphing with electricity were made by different people during the eighteenth century. About 1748 Franklin succeeded in firing spirits by means of a wire across the Schuylkill River, using, as all the other experimenters had done, frictional electricity. In 1753 an anonymous letter was written to Scott's Magazine describing a method by which it was possible to communicate at a distance by electricity. The writer proposed the use of a wire for each letter of the alphabet, that should terminate in pith balls at the receiving end, and under the balls were to be strips of paper corresponding to the letters ofthe alphabet. The message was to be sent by discharging static electricity through the wire corresponding to the first letter of a word when the paper would be attracted to the pith ball and read by the observer. Then the wire corresponding to the second letter of the word was to be charged in like manner, and so on till the whole message was spelled out. This was the first practical (i.e., possible) suggestion for a telegraph. The writer also proposed to have the wires strung on insulators, which was a great advance over the other attempts.
The communication was anonymous, as no doubt, like many others, the author feared the ridicule of his neighbors. It requires a vast amount of moral courage to stand up before the world and openly advocate some new theory that has never come within the experience of any one before. It requires much now, but it required more then; for a man in those days would have been roasted for what in these days he would be toasted. The rank and file of humanity have been opposed to innovations in all ages, but no progress could have been made without innovations. There always has to be a first time. Galileo is said to have been forced to retract, on his knees, some theory he advanced about the motion of the earth, and its relation to the sun and other heavenly bodies. Notwithstanding this retraction the seed-thought sown by Galileo took root in otherminds, which led to the triumph of scientific truth over religious fanaticism.
The writer in Scott's Magazine did not have the opportunity to put his ideas into practice, so the glory of the invention fell to others. Such men as this unknown writer are made of finer stuff, and they stand alone on the frontier of progress. They do not fear the bullets of an enemy half so much as the gibes of a friend. Much of their work is done quietly and without notice, and when something of real importance is worked out theoretically and experimentally, some one seizes upon it and proclaims it from the housetops and attaches to it his name; but perhaps years after the real inventor (the man who taught the so-called inventor how to do it) is dead, some one writes a book that reveals the truth, and then the hero-loving people erect a monument to his memory.
Such a man was our own Professor Joseph Henry, so long the presiding genius at the Smithsonian Institution at Washington. He worked out all the problems of the present American telegraphic system and demonstrated it practically. Everything that made the so-called Morse telegraph a success had long before been described and demonstrated by Henry. Yet with the modest grace that was ingrained in the man he yielded all to the one who was instrumental in constructing thefirst telegraph line between Baltimore and Washington. Great credit is due to such men as Morse and Cyrus W. Field—neither of them inventors, but promoters of great systems of communication that are of unspeakable benefit to mankind. Henry pointed out the way, and Morse carried it into effect. Morse has had no more credit than was due him, but has Henry had as much as is due him? No great invention was ever yet the work, wholly, of one man. We Americans are too apt to forget this.
I shall always remember Henry as a most unassuming, kindly, genial man, and I shall never forget his kindness to me. In 1874 I began my researches in telephony, having applied for a patent for an apparatus for transmitting musical tones telegraphically. This consisted of a means of transmitting musical tones through a wire and reproducing them on a metal plate (stretched on the body of a violin to give it resonance) by rubbing the plate with the hand—the latter being a part of the circuit. The examiner refused the application at first on the ground that the inventor or operator could not be a part of his machine. I took my apparatus and went to Washington, first calling upon Professor Henry, never having met him before. He received me most kindly, and allowed me to string wires from room to room in the institute, and when hehad witnessed the experiments he seemed as delighted as a child. I now brought the patent office official over to the Smithsonian and soon convinced him that the inventor could be a part of his own machine.
The same year I went abroad, and Henry gave me a letter to Tyndall. It was very fortunate for me that he did, for Tyndall was very shy at first, and it was only Henry's letter that gave me a hearing for a moment. The history of the few days that followed this first interview with Tyndall at the Royal Institution would make very interesting reading, if I felt at liberty to publish it. Suffice it to say that he was convinced in a few minutes after he had reached the experimental stage that not all my work had been anticipated by Wheatstone, as he asserted before seeing the experiments. Wheatstone had transmitted the tones of a piano, mechanically, from one room to another by a wooden rod placed upon the sound-board and terminating in another room in contact with another sound-board. But this was very different from transmitting musical tones and melodies from one city to another through a wire, as I could do with my electrotelephonic apparatus.
It is a curious fact that the world is divided into two great classes, leaders and followers. Or we might say, originators and copyists; the former division being very small, while thelatter is very large. As late as 1820 the European philosophers were trying to construct a telegraphic system based upon two ideas, announced a long time before, to wit, the use of static or frictional electricity, and a wire for every letter. It does not seem to have occurred to any one to devise a code consisting of motions differently related as to time, and to use simply one wire.
In 1819 Oersted discovered the effect of a galvanic current on a magnetic needle, and published a pamphlet concerning his discovery. This stimulated others, and Ampère applied it to the galvanometer the same year. Arago applied it to soft iron, and here was the germ of the electromagnet. We see that as far back as 1820 we had the galvanic battery and the electromagnet, the two great essentials of the modern telegraph.
However, there remained another great discovery to be made before these elements could be utilized for telegraphic purposes. One cell of battery was used, and the magnet was made by winding one layer of wire spirally around the iron, so that each spiral was out of touch with its neighbor. Barlow of England, a Fellow of the Royal Society, tried the effect of a current through a wire 200 feet long, and found that the power was so diminished that he was discouraged, and in a paper gave it as his opinion that galvanism was of no use fortelegraphing at a distance. This paper stimulated others, and it was reserved for our own Joseph Henry, already referred to, to show not only how to construct a magnet for long-distance telegraphy, but also how to adapt the battery to the distance. He showed us that by insulating the wire and using several layers of whirls, instead of one, and by using enough cells of battery coupled up in series to get more voltage, as we now express it, it was possible to transmit signals to a distance. He not only set forth the theory, but he constructed a line of bell-wire 1060 feet long and worked his magnet by making the armature strike a bell for the signals, which is the basis of the modern "sounder."
Nothing was needed but to construct a line and devise a code to be read by sound, to have practically our modern Morse telegraph. This line was constructed in 1831. In 1835 Henry, who was then at Princeton, constructed a line and worked it as it is to-day worked, with a relay and local circuit, so that at that period all the problems had been worked out. But, like the speaking-telephone in its early inception, no one appreciated its real importance. Henry himself did not think it worth while to take out a patent. Two years later the Secretary of the Treasury sent out a circular letter of inquiry to know if some system of telegraphic communication could not be devised. Thelearned heads of the Franklin Institute of Philadelphia, the oldest scientific society in America, advised that a semaphore system be established between New York and Washington, consisting of forty towers with swinging arms, the same as used in the days of Wellington. Among other replies to the circular letter of the secretary was one from Samuel F. B. Morse. Morse was not a scientist or even an inventor, at least not at that time. He was an artist of some note. In 1832, while crossing the ocean, Morse, in connection with one Dr. Jackson of Boston, devised a code of telegraphic signs intended to be used in a chemical telegraph system.
Some years later Morse adapted Henry's signal-instrument to a recorder, called the Morse register, and this was the instrument used in the early days of the Morse telegraph.
What Morse seems to have really invented was the register, which made embossed marks on a strip of paper, and the code of dots and dashes representing letters, now known as the Morse alphabet, although this latter is questioned. Morse took his apparatus to Washington and exhibited it to the members of Congress in the year 1838, but it was four years before a bill was passed that enabled him to try the experiment between Baltimore and Washington. We will let him describe in hisown words the closing day of Congress. He says:
"My bill had indeed passed the House of Representatives and it was on the calendar of the Senate, but the evening of the last day had commenced with more than 100 bills to be considered and passed upon before mine could be reached. Wearied out with the anxiety of suspense, I consulted one of my senatorial friends. He thought the chance of reaching it to be so small that he advised me to consider it as lost. In a state of mind which I must leave you to imagine, I returned to my lodgings to make preparations for returning home the next day. My funds were reduced to the fraction of a dollar. In the morning, as I was about to sit down to breakfast, the servant announced that a young lady desired to see me in the parlor. It was the daughter of my excellent friend and college classmate, the commissioner of patents, Henry L. Ellsworth. She had called, she said, by her father's permission, and in the exuberance of her own joy, to announce to me the passage of my telegraph bill at midnight, but a moment before the Senate adjourned. This was the turning-point of the telegraph invention in America. As an appropriate acknowledgment of the young lady's sympathy and kindness—a sympathy which only a woman can feel and express—I promised that the first dispatch by the firstline of telegraph from Washington to Baltimore should be indited by her; to which she replied: 'Remember, now, I shall hold you to your word.' About a year from that time the line was completed, and, everything being prepared, I apprised my young friend of the fact. A note from her inclosed this dispatch: 'What hath God wrought?' These were the first words that passed on the first completed line in America."
The first telegraph-line in America was put into operation in the spring of 1844 at the beginning of Polk's administration. I remember as a boy having the two cities, Baltimore and Washington, pointed out to me on the map, and how the story of the telegraph impressed me. Congress appropriated $30,000 for the construction of the line, and $8000 to keep it running the first year. It was placed under the control of the postmaster-general, and the line was thrown open to the public. The tariff was fixed at one cent for every four words. It was open for business on April 1, 1844, and for the first few days the revenue was exceedingly small. On the morning of the first day a gentleman came in and wanted to "see it work." The operator told him that he would be glad to show it at the regular tariff of one cent for four words. The gentleman grew angry and said that he was influential with the administration, and that if he did notshow him the working free of charge he would see to it that he lost his job. His bluff did not succeed. The operator referred him to the postmaster-general, and thus the stormy interview ended. No patrons came in for the next three days, but a great number stood around hoping to see the instrument start up, but no one was willing to invest a cent—probably from fear of being laughed at.
On the fourth day the same gentleman who had threatened the young man with dismissal came back and invested a cent, and this was the first and only revenue for four days. The message that was sent only came to one-half cent, but as the operator could not make change the stranger laid down the cent and departed. His name ought to be known to fame as the first man patron of the telegraph.
The operation of the Morse telegraph is very simple if we grant all that has gone before. All that is needed is the wire, the battery, and the key, as shown inFig. 2(page 99), and a relay—an extra electromagnet which receives the electric current and by its means puts into or out of action a small local battery on a short circuit in which is placed the receiving or recording apparatus. Thus we have a wire starting from the earth in New York and passing through a battery, a key and a relay, and thence to Boston on poles, with insulators on which the wire is strung, and through anotherinstrument, key and battery in Boston, the same as at the New York end, and into the ground, leaving the earth to complete one-half of the circuit. When the keys at both ends are closed the batteries are active and the armatures or "keepers" are attracted so that the armature levers rest on the forward stops. (See diagramFig. 2.) If either one of the keys is opened the current stops flowing and the magnetism vanishes from all the electromagnets on the line, and a spring or retractile of some kind pulls the armatures away from the magnets and the levers rest on their back stops. In this way all the levers of all the magnets are made to follow the motions of any key. If there are more than two magnets in circuit (and there may be twenty or more) they all respond in unison to the working of one key, so that when any one station is sending a dispatch all the other stations get it.
Fig. 2.Fig. 2.A gives a diagram view of a Morse telegraph-line with three stations. B is the battery; C C C, the transmitting keys in the three offices; D D D, the relay magnets; E E E, the armatures that are actuated by the magnets.
A gives a diagram view of a Morse telegraph-line with three stations. B is the battery; C C C, the transmitting keys in the three offices; D D D, the relay magnets; E E E, the armatures that are actuated by the magnets.
But there is a "call" for each office, so that the operator only heeds the instrument when he hears his own call. Operators become so expert in reading by sound that they may lie down and sleep in the room, and, although the instrument is rattling away all the time, he does not hear it till his own call is made, when he immediately awakes.
In the old days messages were received on slips of paper by the Morse register by means of dots and dashes. Gradually the operator learned to read by sound, till now this mode of receiving is almost universal the world over. Reading by sound was of American origin. It is a spoken language, and when one becomes accustomed to it it is like any other language. This code language has some advantages over articulate speech, as well as many disadvantages. A gentleman who was connected with a Louisville telegraph office told me that one of the best operators he ever knew was as deaf as a post. He would receive the message by holding his knee against the leg of the table upon which the sounder was mounted, and through the sense of feeling receive the long and short vibrations of the table, and by this means read as well or better than through the ear, because he was not distracted by other sounds.
A story is told of the late General Stager that at one time he was on a train that waswrecked at some distance from any station. He climbed a telegraph pole, cut the wire and by alternately joining and separating the ends sent a message, detailing the story of the wreck, to headquarters, and asked for assistance. He then held the two ends of the wire on each side of his tongue and tasted out the reply—that help was coming. Any one who has ever tasted a current knows that it is very pronounced.
A story similar to this is told of the early days when the Bain chemical system was used between Washington City and some other point. This system made marks on chemically-prepared paper; as the current passed through it left marks on the paper from the decomposition of the chemicals. Some of the preparations emitted an odor during the time that the current passed. The occurrence to which we refer took place at presidential election time. At some station out of Washington an operator was employed who had a blind sister, and this sister knew the Morse alphabet well before she became blind. One evening a signal came to get ready for a message containing the returns from the election. In the hurry, and just as the message had started, the lamp was upset and they were in total darkness—at least, the brother was. The sister, poor girl, had been in darkness a long time. The blind sister leaned over the stylus throughwhich the current flowed to the paper and smelled out as well as spelled out the message, and repeated it to her astonished brother.
By the old semaphore system the motions were sensed through the eye as well as the early method of cable signaling. It will be seen from the above that the Morse code may be communicated through any one of the five senses.
With but few exceptions the Morse code is the one almost universally used the world over. As it is used in Europe, it is slightly changed from our American code, but they all depend upon dots, dashes, and spaces, related in different combinations, for the different letters. Notwithstanding its universal use it is not free from serious difficulties in transmission unless it is repeated back to the sender for correction; and then in some cases it is impossible to be sure, owing to difficulties of punctuation and capitalizing, and the further difficulty of running the signals together, caused, it may be, by faulty transmission, induced currents from other wires, "swinging crosses" or atmospheric electricity. Sometimes it is a psychological difficulty in the mind of the receiving-operator. The telegraph companies have to suffer damages from all these and many other unforeseen causes.
Prescott tells some curious things that happened in the early days, growing out of the peculiarities of the receiving-operator. Atone time he was reporting by telegraph one of Webster's speeches made at Albany in 1852 in which there were many pithy interrogative sentences, and he was desirous of having the interrogation-points appear. So to make sure, whenever he wished an interrogation-point he said "question" at the end of almost every sentence. Next day he was horrified on reading the speech to see the ends of the sentences bristling with the word "question."
Some time back in the fifties a gentleman in Boston telegraphed to a house in New York to "forward sample forks by express." The message when received by the New York merchant read: "Forward sample for K. S. by express." The New York merchant did not know who K. S. was, nor did he gather from the dispatch what kind of sample he wanted. So he went to the telegraph office to have the matter cleared up. The Boston operator repeated the message, saying "sample forks." "That's the way I received it and so delivered it—sample for K. S.," said New York. "But," says Boston, "I did not say for K. S.; I said f-o-r-k-s." New York had read it wrong in the start and could not get it any other way. "What a fool that Boston fellow is. He says he did not say for K. S., but for K. S." Boston had to resort to the United States mail before the mystery was solved.
Curiously enough, the old method of recording the dots and dashes on the paper strip was not so reliable as the present mode of reading by sound. A man can put his individuality to some extent into a sounder, and when one becomes used to his style it is much easier to read him accurately by sound than by the paper impressions. Some people never could learn to read either by paper or sound. An instance of this kind is given of a middle-aged man who was employed by a railroad company as depot master and telegraph operator, in the old days of the paper strip. One day he rushed out and hailed the conductor of a train that had just pulled into the station, and told him that —— train had broken both driving-wheels and was badly smashed up. The conductor could read the mystic symbols, so he took the tape and deciphered the dispatch as follows: "Ask the conductor of the Boston train to examine carefully the connecting-rods of both driving-wheels, and if not in good condition to await orders." It is further related of this same operator that when he got into real difficulty with his "tape" he used to run over to the regular commercial office to have his messages translated. One day he rushed into his neighbor's office trailing the tape behind him and saying: "I am sure an awful accident has happened by the way the message was rattled off." A playful dog had torn off a large part of the strip as it trailed along, soonly a part was left. It read, "Good morning, Uncle Ben. When are you——" The dog had swallowed the balance of the dispatch.
Sometimes the Morse code is not only funny but disastrous. A gentleman wanted to borrow money of some capitalists who, not knowing his financial standing, telegraphed to a banker who they knew could post them. They received an answer, "Note good for large amount." The gentleman borrowed a "large amount," but afterward when it came to be investigated it was found that the dispatch was originally written "not," instead of "note," which made "all the difference in the world."
It has been stated that any one of the five senses may be called into service to interpret the Morse code into words and ideas. A story is told by Mr. Prescott that he says is true, as he knew the party. A friend of his, by name Langenzunge, who knew the Morse code, had served under General Taylor (who at this time was President) at Palo Alto, in Mexico. The general had just promised him an office; soon after he left Washington for the west over the Baltimore and Ohio on a freight train; the President was taken seriously ill, and his friend hearing of it was troubled not only because he loved the old general, but on account of the change in his own prospects. The train stopped somewhere on the Potomac at midnight and remained there for four hours. Uneasy and sad, he wandered down the track and climbed a pole, cut the wire and placed the ends each side of his tongue and tasted out the fatal message—"Died at half-past ten." The shock (not the electric) was so great that he almost fell from the pole.
What a situation! A man climbs a pole at midnight miles from the sick friend he loves, puts his tongue to inanimate wire, and is told in concrete language—through the sense of taste—that his friend is dead. This is only one of the many, many wonderful episodes of the telegraph.
"It never rains but it pours." Almost simultaneously with the demonstration of the Morse telegraph other types were devised. There were the needle systems of Cooke and Wheatstone, the chemical telegraph of Alexander Bain, and soon the printing telegraph of House, and later that of Hughes. The latter is in use on the continent of Europe, and a modification of it has a very limited use on some American lines. The Bain telegraph used a key and battery the same as the Morse system, but it did not depend upon electromagnetism as the Morse system does. When in operation a strip of paper was made to move under an iron stylus at the receiving-end of the line. The paper was saturated with some chemical that would discolor by the electrolytic action of the current. When a message was sent the paper was set to moving by a clock mechanism or otherwise, under the stylus that was pressing on the paper as it passedover a metal roller or bed-plate. The transmitting-operator worked his key precisely as in sending an ordinary message by the Morse system. The effect was to send currents through the receiving-stylus chopped into long or short marks, or the dots and dashes of the Morse code, and recorded on the tape in marks that were blue or brown, according to the chemical used. A few lines were established in this country on the Bain system, but it never came into general use.
A number of systems, called "automatic," grew out of the Bain system. Bain himself devised, perhaps, the first automatic telegraph. The fundamental principle of all automatic telegraphs depends upon the preparation of the message before sending, and is usually punched in a strip of paper and then run through between rollers that allow the stylus to ride on the paper and drop through the holes that represent the dots and lines of the Morse alphabet. Every time the stylus drops through a hole in the paper it makes electrical contact and sends a current, long or short, according to the length of the hole. The object of the automatic system was to send a large amount of business through a single wire in a short time. It does not save operators, as the messages have to be prepared for transmission, and then translated at the receiving-end and put into ordinary writing for delivery.
The automatic system is not used except for special purposes, and the one that seems to be the most favored is that of Wheatstone. The system is in use in England and in America to a limited degree.
Early in the history of the telegraph a printing system was devised. Wheatstone and others had proposed systems of printing telegraphs in Europe, but these never passed the experimental stage. The first printing telegraph introduced in America was invented by Royal E. House of Vermont, and first introduced in 1847 on a line between Cincinnati and Jeffersonville, a distance of 150 miles. In 1849 a line for commercial use was established between New York and Philadelphia, and for some years following many lines were equipped with the House printing telegraph instrument. The late General Anson Stager was a House operator at one time. All printing telegraph instruments, while differing greatly in detail, have certain things in common, to wit: a means for bringing the type into position, an inking device, a printing mechanism, a paper feed, and a means for bringing the type-wheels into unison. There are two general types of printing instruments, the step-by-step, and the synchronously moving type-wheels. The House printer was a step-by-step instrument and consisted of two parts, a transmitter and a receiver. The transmitter consists of a keyboard like a piano, with twenty-eight keys. These keys are held in position by springs. Under the keys is a cylinder having twenty-eight pins on it corresponding to the twenty-six letters of the alphabet and a dot and a space. This cylinder was driven by some power. In those days it was by man-power. It was carried by a friction, so that it could be easily stopped by the depression of any one of the keys that interfered with one of the pins. One revolution of the cylinder would break and close the current twenty-eight times, making twenty-eight steps.
The receiving-instrument consisted of a type-wheel and means for driving it. It was somewhat complicated, and can only be described in a general way. If the cylinder of the transmitter was set to rotating it would break and close twenty-eight times each revolution. (There were fourteen closes and fourteen breaks, each break and each close of the current representing a step.) The type-wheel of the receiver was divided into twenty-eight parts, having twenty-six letters and a dot and space, each break moved it one step and each close a step; so that if the cylinder, with its twenty-eight pins, started in unison with the type-wheel, with its twenty-eight letters and spaces, they would revolve in unison. The keys were lettered, and if any one was depressed the pin corresponding to it on thecylinder would strike it and stop the rotation of the cylinder, which stopped the breaking and closing of the circuit, which in turn stopped the rotation of the type-wheel—and not only stopped it, but also put it in a position so that the letter on the type-wheel corresponding to the letter on the key that was depressed was opposite the printing mechanism. The printing was done on a strip of paper, which was carried forward one space each time it printed. The printing mechanism was so arranged that so long as the wheel continued to rotate it was held from printing, but the moment the type-wheel stopped it printed automatically.
The messages were delivered on strips of paper as they came from the machine.
In 1855 David E. Hughes of Kentucky patented a type-printing telegraph that employed a different principle for rotating the type-wheel. The electric current was used for printing the letters and unifying the type-wheels with the transmitting-apparatus. The transmitter, cylinder, and the type-wheel revolved synchronously, or as nearly so as possible, and the printing was done without stopping the type-wheel. Whenever a letter was printed the type-wheel was corrected if there was any lack of unison.
This type of machine in a greatly improved form is still used on some of the WesternUnion lines, especially between New York, Boston, Philadelphia, and Washington. It is also in use in one of its forms in most of the European countries.
Although the printing and automatic systems of telegraphing are used in America to some extent, the larger part is done by the Morse system of sound-reading and copying from it, either by pen or the typewriter. In the early days only one message could be sent over one wire at the same time, but now from four to six or even more messages may be sent over the same wire simultaneously without one message interfering with the other. Like most other inventions, many inventors have contributed to the development of multiple transmission, till finally some one did the last thing needed to make it a success. The first attempts were in the line of double transmission, and many inventors abroad have worked on this problem.
Moses G. Farmer of Salem, Mass., proposed it as early as 1852, and patented it in 1858. Gintl, Preece, Siemens and Halske and others abroad had from time to time proposed different methods of double transmission, but no one of them was a perfect success. When theline was very long there was a difficulty that seemed insurmountable. In the common parlance of telegraphy, there was a "kick" in the instrument that came in and mutilated the signals. About 1872 Joseph B. Stearns of Boston made a certain application of what is called a "condenser" to duplex telegraphy that cured the "kick," and from that time to this it has been a success. Farther along I will tell you what occasioned this "kick" and how it was cured. If this or some other method could be applied as successfully to cure the many chronic "kickers" in the world it would be a great blessing to mankind.
It has always been a mystery to the uninitiated how two messages could go in opposite directions and not run into one another and get wrecked by the way. If you will follow me closely for a few minutes I will try to tell you.
We have already stated that an electromagnet is made by winding an insulated wire around a soft iron core. If we pass a current of electricity through this wire the core becomes magnetic, and remains so as long as the current passes around it. In duplex telegraphy we use what is called a differential magnet. A differential electromagnet is wound with two insulated wires and so connected to the battery that the current divides and passes around the iron core in opposite directions.Now if an equal current is simultaneously passed through each of the wires of the coil in opposite directions the effect on the iron will be nothing, because one current is trying to develop a certain kind of polarity at each pole of the magnet, while the current in the other wire is trying to develop an opposite kind in each pole. There is an equal struggle between the two opposing forces, and the result is no magnetism. This assumes that the two currents are exactly the same strength.
If we break the current in one of the coils we immediately have magnetism in the iron; or if we destroy the balance of the two currents by making one stronger than the other we shall have magnetism of a strength that measures the difference between the two.
Without specifically describing here the entire mechanism—since this is not a text-book or a treatise—we may say that a duplex telegraph-line is fitted with these differentially wound electromagnets at every station. When Station A (Fig. 3) is connected to the line by the positive pole of its battery, Station B will have its negative pole to line and its positive to earth. When A depresses his key to send a message, half the current passes by one set of coils around his differential magnet through a short resistance-coil to the earth, and the other half by the contrary coil around the magnet to the line, and so to Station B.The divided current does not affect A's own station, being neutralized by the differential magnet, but it does affect B, whose instrument responds and gives him the message.
Now B may at the same time send a message to A by half of his own divided current from his own end of the line.
Fig. 3.Fig. 3.Represents a duplex 500-mile telegraph-line. A and B are the two terminal stations; B B´, the batteries; K K´, the keys; D D´, the small resistance-coils, equal to the battery-resistance when the latter is not in circuit; R R´, resistances each equal to the 500-mile line; and C C´, condensers giving the artificial lines R R´ the same capacity as the 500-mile line.
Represents a duplex 500-mile telegraph-line. A and B are the two terminal stations; B B´, the batteries; K K´, the keys; D D´, the small resistance-coils, equal to the battery-resistance when the latter is not in circuit; R R´, resistances each equal to the 500-mile line; and C C´, condensers giving the artificial lines R R´ the same capacity as the 500-mile line.
The puzzle to most people is: How can the signals pass each other in different directions on the same wire? But the signals do not have to pass each other. In effect, they pass; but in fact, it is like going round a circle—the earth forming half. A sends his message over the line to B. B sends his message to A through the earth and up A's ground-wire. The operative who is sending with positive pole to linepusheshis current through—so tospeak—while the operative who is sending with the negative pole to linepullsmore current in the same direction through the line whenever he closes his key.
This may not be a strictly scientific statement; but, as long as we speak of a "current" flowing from positive to negative poles (which is the invariable course electricity takes), it is the way to look at the matter understandingly.
The short "resistance-coil" at each end, fortified by a "condenser" made of many leaves of isolated tin-foil, to give it capacity, offers precisely the same resistance to the current as the 500 miles of wire line; so that the twin currents that run around the differential magnet exactly neutralize each other and make no effect in the office the message starts from; while one of them takes to the earth, and the other to the line to carry the message.
This condenser is necessary, because the short resistance-coil affects the current immediately, while the long line with its greater amount of metal does not give the same amount of resistance till it is filled from end to end, which requires a fraction of a second. During this time, however, more current is passing through the differential coil connected with the line than through the short resistance-coil; and the unequal flow causes the relay armature to jump, or "kick." The condenser, with the many leaves of tin-foil, supplies the greater metal surface to be traversed by the short line current, causes the flow to be equal in both circuits at all times, and thus cures the "kick." It is this quality of a condenser that enables us to give to an artificial line of any resistance all the qualities, including capacity, and exhibit all the phenomena of a real line of any length, and it was this quality that enabled Mr. Stearns to take the "kick" out of duplex transmission and thus change the whole system, which created a new era in telegraphy.
We have just spoken of the "capacity" of a circuit, and stated that it was determined by the mass of metal used. This capacity is measured by a standard of capacity that is arbitrary and consists of a condenser, constructed so that a given amount of surface of tin-foil may be plugged in or out. The practical unit of capacity is called the micro-farad, the real unit is the farad, and takes its name from Faraday.
But let us go back to multiple systems of transmission. There are many other systems of simultaneous transmission aside from the duplex, and all of them are classed under the general head of multiple telegraphy. First there is the quadruplex, that sends two messages each way simultaneously, making one wire do the work of four single wires—asthey were used at first. The quadruplex is very extensively used by the Western Union Telegraph Company and others. It would be difficult to explain it in a popular article, so we will not attempt it. There is another form of multiple telegraph that was used on the Postal Telegraph line when it first started—which was invented and perfected by the writer—that can be more easily explained.
In 1874 I discovered a method of transmitting musical tones telegraphically, and the thing that set my mind in that direction was a domestic incident. It is a curious fact that most inventions have their beginnings in some incident or observation that comes within the experience of some one who is able to see and interpret the meaning of such incidents or observations. I do not mean to say that inventions are usually the result of a happy thought, or accident; the germ may be, but the germ has to have the right kind of soil to take root in and the right kind of culture afterward. It is a rare thing that an invention, either of commercial or scientific importance, ever comes to perfection without hard work—midnight oil and daylight toil; and it is rarely, if ever, that a discovery or an invention based upon a discovery does not have, sooner or later, a practical use, although we sometimes have to wait centuries to find it put. We had to wait forty-four years afterthe galvanic battery was discovered before it became a useful servant of man. It was fifty years or more after the discovery by Faraday of magneto-electricity before it found a useful application beyond that of a mere toy, but now it is one of the most useful servants we have, as shown in its wonderful development in electric lighting and electric railroads, to say nothing of its heating qualities and the useful purpose it serves in driving machinery. The interesting discoveries of Professor Crookes in passing a current of electricity through tubes of high vacua waited many years before they found a practical use in the X-ray, that promises to be of great service in medicine and surgery.
The transmission of musical harmonies telegraphically, while in itself of great scientific interest, was of no practical use, but it led to other inventions, of which it is the base, that are transcendently useful in every-day life. The transmission of harmonic sounds by electricity underlies the principle of the telephone. There is a vast difference, in principle, between the transmission of simple melody, which is a combination of musical tones transmitted successively—one tone following another—and the transmission of harmony, which involves the transmission of two or more tones simultaneously. The former can be transmitted by a make-and-break current. In the latter case one tone has to be superposed upon another and must be transmitted with a varying but a continuously closed current. I make a distinction between a closed circuit and a closed current. In the case of the arc-light the circuit is open (that is, broken), technically speaking, but the current is still flowing. The reason why the Reiss and other metallic contact telephone transmitters cannot successfully be used for telephone purposes is that metal points will not allow of sufficient separation of the transmitting points without breaking the current as well as the circuit. Carbon contacts admit of a much wider separation without actually stopping the flow of the current, which latter is a necessity for perfect telephonic transmission, and it was the use of carbon that made that form of transmitter a success.
There are other forms, or at least one other form that does not depend upon the length of the voltaic arc formed when the electrodes are separated. Of this we will speak another time. Now let us go back to the domestic incident referred to above.
One evening in the winter of 1873-4 I came home from my laboratory work and went into the bathroom to make my toilet for dinner. I found my nephew, Mr. Charles S. Sheppard, together with some of his playmates, taking electrical "shocks" from a little medical induction-coil that I heard humming in the closet. He had one terminal of the coil connected to the zinc lining of the bathtub—which was dry at that time—while he held the other in his left hand, and with his right was taking shocks from the lining of the tub by rubbing his hand against the zinc. I noticed that each time he made contact with the tub, as he rubbed it for a short distance, a peculiar sound was emitted from under his hand, not unlike the sound made by the electrotome that was vibrating in the closet. My interest was immediately aroused, and I took the electrode out of his hand and for some time experimented with it, going to the cupboard from time to time to change the rate of vibration of the electrotome, and thus change the quality of the sound. I noticed that the sound or tone under my hand, if it could be so called, changed with each change of the rate of vibration. The thing that most interested me was that the peculiar characteristics of the noise were reproduced. In those few minutes I laid out work enough for years of experiment, and as a result I was late to dinner.
This discovery opened up to my mind the possibility of three things—the transmission of music and of speech or articulate words through a telegraph-wire, and the transmission of a number of messages over a single wire. I constructed a keyboard consisting ofone octave and made a set of reeds tuned to the notes of the scale, and then when some one would play a melody I could reproduce it in two ways: One by placing my body in the circuit and rubbing a metal plate—it might be the bottom of a tin pan, a joint of stovepipe or otherwise—anything that was metal and would vibrate would give the effect. Another way was to connect an electromagnet (having a diaphragm or reed across its poles) in the circuit at the receiving-end and mount it on some kind of a soundboard. I made a great number of different kinds of receivers that were capable of receiving either musical or articulate sounds, as has many times been proven by experiment. I carried two sets of experiments along together; the one looking toward a system of multiple telegraphy and the other the transmission of articulate speech. Let us first look into the multiple telegraph and take the other up under the head of the telephone.
When the electrical keyboard was completed I found that I could transmit not only a melody but a harmony; that more than one tone could be transmitted simultaneously. This discovery opened up a long series of experiments with the view of sending a number of messages simultaneously by means of musical tones differing in pitch. I had already demonstrated that several tones could be transmitted at once, but they would speak all alike(with the same loudness) on the receiving-instrument. I now went to work on an instrument that responded for one note only and succeeded beyond my expectations. I made three different kinds of receiving-instruments. The first was a steel strap about eight inches long by three-eighths wide. This strap was mounted in an iron frame in front of an electromagnet. A thumbscrew enabled me to stretch the strap till it would vibrate at the required pitch. If, for instance, the sending-reed vibrated at the rate of 100 times per second and the strap of the receiver was stretched to a tension that would give 100 vibrations per second when plucked, it would then respond to the vibrations of the sending-reed but not to those of another reed of a different rate of vibration. If we take mounted tuning-forks tuned in pairs of different pitches, say four pairs, so that each fork has a mate that is in exact accord with it, and place them all in the same room, and sound one of them for a few seconds and then stop it, upon examining the other forks you will find all of them quiet except the mate of the one that was sounded. This one will be sounding. If we now sound four of the forks and then stop them the other four will be sounding from sympathy because the mate of each one of them has been sounded. If only two forks differing in pitch are sounded only two of the otherswill sound in sympathy. In the first case only one set of sound-waves were set up in the air, and the fork that found itself in accord with this set responded. When four forks differing in pitch were sounded there were four sets of tone-waves superposed upon each other existing in the air, so that each of the remaining forks found a set of waves in sympathy with its own natural rate of vibration and so responded.
Now apply this principle to the harmonic telegraph and you can understand its operation. At the transmitting-end of a line of wire there are a certain number of forks or reeds kept vibrating continuously. These reeds each have a fixed rate of vibration and bear a harmonic relation to each other so as not to have sound-interference or "beats." At the receiving-end of the line there are as many electromagnets as there are transmitting-reeds, and each magnet has a reed or strap in front of it tuned to some one of the transmitting-reeds, so that each transmitting-reed has a mate in exact harmony with it at the receiving-end of the line. Keys are so arranged at the transmitting-end as to throw the tones corresponding to them to line when depressed. In other words, when the key belonging to battery B and vibrator 1 is depressed (seeFig. 4) the effect is to send electrical pulsations through the line corresponding in rate per second to that of the vibrator. The same is true of battery B´ and vibrator 2. During the time any key is depressed—we will say of tone No. 1—this tone will be transmitted through the line and be reproduced by its mate—the one tuned in accord with it—at the receiving-station. By a succession of long and short tones representing the Morse code a message can be sent. Numbers two, three and four might be sending at the same time, but they would not interfere with number one or with each other. In 1876-7 the writer succeeded in sending eight simultaneous messages between New York and Philadelphia by the harmonic method.