PRELIMINARY: NOTICE OF THE TELEPHONE IN RELATION TO WIRELESS TELEGRAPHY.
"Give me the ocular proof,
Make me see't; or, at least, so prove it,
That the probation bear no hinge, nor loop,
To hang a doubt on."
WE have now arrived at a period in the history of our subject at which experiments begin to assume a character more hopeful of practical results. All that went before was more or less crude and empirical, and could not be otherwise from the very necessities of the case. The introduction of the telephone in 1876 placed in the hands of the electrician an instrument of marvellous delicacy, compared with which the most sensitive apparatus hitherto employed was as the eye to the eye aided by the microscope. Thus, Prof. Pierce of Providence, Rhode Island, has found that the Bell telephone gives audible signals with considerably less than the one-hundred-thousandth part of the current of a single Leclanché cell. In testing resistances with a Wheatstone bridge, the telephone is far more sensitive than the mirror galvanometer; in ascertaining the continuity of fine wire coils it gives the readiest answers; and for all the different forms of atmospheric electrical discharges--and they are many--it has a language of its own, and opens up to research a new field in meteorology.
The sound produced in the telephone by lightning, even when so distant that only the flash can be seen in the horizon, and no thunder can be heard, is very characteristic--something like the quenching of a drop of molten metal in water, or the sound of a distant rocket; but the remarkable circumstance for us in this history is, that this sound is always heard just before the flash is seen, showing that there is an inductive disturbance of the electricity overhead, due to the distant concentration preceding the disruptive discharge. Thus, on November 18, 1877, these peculiar sounds were heard in Providence, and the papers next morning explained them by reporting thunderstorms in Massachusetts. Sounds like those produced by lightning, but fainter, are almost always heard many hours before a thunderstorm actually breaks. 42 The Bell telephone was tried for the first time on a wire from New York to Boston on April 2, 1877, and soon afterwards its extraordinary sensitiveness to induction currents, and currents through the earth (leakages) from distant telegraph circuits, began to be observed. 43 Thus, in August 1877, Mr Charles Rathbone of Albany, N.Y., had been experimenting with a Bell telephone which was attached to a private telegraph line connecting his house with the Observatory. One evening he heard some singing which he thought came from the Observatory, but found on inquiry that that was not the case. He then carefully noted what followed, and next morning sent a note to the newspapers stating the facts and giving the names of the tunes which he had heard. This elicited the information that the tunes were those of an experimental concert with Edison's singing telephone over a telegraph wire between New York and Saratoga Springs. It was then resolved to follow up this curious discovery, and, accordingly, when Edison's agent gave another concert in Troy, arrangements were made to observe the effects. A wire running from Albany to Troy alongside the Edison wire was earthed with a Bell telephone in circuit at each end. The concert was heard as before, the music coming perfectly clear, and the tunes distinguishable without the least difficulty.
Later in the evening the instruments were put in circuit on one of the wires running from Albany to New York. Again the music was heard, and much louder, so that by placing the telephone in the centre of the room persons seated around could hear with perfect distinctness.
These observations were made on six separate occasions between August 28 and September 11, and, strangely enough, two other and independent observers in Providence, 200 miles away, noted the same effects on five out of the six dates given by Mr Rathbone. 44 Dr Channing, one of the observers in Providence, has published a very interesting account 45 of his observations, from which I will make a few extracts. During five evenings in the latter part of August and first part of September 1877 concerts were given in the Western Union Office, N.Y., for the benefit of audiences in Saratoga, Troy, and Albany respectively. The performers sang or played into an Edison musical telephone, actuated by a powerful battery, and connected with one or other of the above-named places by an ordinary telegraph line, with return through the ground.
In Providence, on the evening of the first concert, Dr Channing and a friend were conversing through Bell telephones over a shunt wire, made by grounding one of the American District Telegraph wires at two places, a quarter of a mile apart, through the telephones and several hundred ohms resistance. At about half-past eight o'clock they were surprised by hearing singing on the line, at first faint, but afterwards becoming clear and distinct. Afterwards, during that and subsequent evenings, various airs were heard, sung by a tenor or soprano voice, or played on the cornet. On investigation, the music heard proved to be the same as that of the Edison concerts performed in New York.
The question how this music passed from the New York and Albany wire to a shunt on the District wire in Providence is of scientific importance. The Edison musical telephone consists of an instrument which converts sound waves into galvanic waves at the transmitting station, and another apparatus which reconverts galvanic waves into sound waves at the receiving station. The battery used in these concerts consisted of 125 carbon-bichromate cells (No. 1½), with from 1000 to 3000 ohms resistance interposed between the battery and the line. The line wire extended from the Western Union office, viâ the Harlem Railway, to Albany. On the same poles with this Albany wire, for sixteen miles, are carried four other wires, all running to Providence, and also, for eight miles, a fifth wire from Boston, viâ New London, to Providence. All these lines, including the Albany wire, are understood to have a common earth connection at New York, and to be strung at the usual distance apart, and with the ordinary insulation.
At Providence six New York and Boston wires run into the Western Union office on the same poles and brackets for the last 975 feet with an American District wire. This wire belongs to an exclusively metallic circuit of four and a half miles, having, therefore, no earth connection. Finally, in a shunt on this wire, the telephones were placed as before described.
It will thus be seen that the music from the Albany wire passed first to the parallel New York--Providence wires; secondly, from these to a parallel District wire in Providence; and thirdly, through a shunt on the District wire to the telephones.
This transfer may have taken place by induction, by cross-leakage, or, in the first instance, in New York by a crowded ground connection; but in the transfer in Providence from the New York--Boston to the District wire there was no common ground connection, and it is difficult to suppose that sufficient leakage took place on the three brackets and three poles (common to the New York and District wires) to account for it. Without wholly rejecting the other modes of transfer, Dr Channing ascribes to induction the principal part in the effects.
The next question arises, What proportion of the electrical force set in motion in New York could have reached the listeners on the short shunt line in Providence? Whether induction or cross-leakage or crowded ground was concerned, who will say that the New York--Providence wires had robbed the Albany wire of one-tenth or even one-hundredth of its electrical force? When this reached Providence, did the New York wires in the course of 975 feet give up to the District wire one-tenth or one-hundredth of their force? Lastly, when the District circuit had secured this minute fraction, did the shunt, with its 500 ohms resistance as against the few ohms of the shunted quarter-mile, divert one-hundredth part of this minute fraction from the District wire? Plainly, the music reproduced in the Providence telephone did not require one ten - thousandth, nor one hundred-thousandth, of the force originally imparted to the Albany wire.
In December 1877 Prof. E. Sacher of Vienna undertook some careful investigations with a view of measuring the inductive effect in telephone circuits. He found that signals from three Smee cells sent through one wire, 120 metres long, could be distinctly heard in the telephone on another and parallel wire 20 metres distant from it. 46 Early in 1879 M. Henri Dufour tried similar experiments, and with the same results. Two covered copper wires were stretched parallel over a length of 15 metres, and at distances apart varying from 15 to 45 centimetres. In connection with one of the wires were the battery and the ordinary Morse apparatus, the gas-pipes being used to complete the circuit. The ends of the other wire were joined to the telephone so as to form a complete metallic circuit. The current employed produced a deflection of 600 on the galvanometer. Under these conditions all the motions of the key were distinctly heard in the telephone, and the author was satisfied that a telegraphist would have understood the signals, even when the distance between the two wires was 45 centimetres. 47 When we consider the shortness of these wires, the effects are sufficiently striking; but before this, equally striking results had been obtained on actual telegraph lines, where there was no battery, and where the infinitesimal currents produced by speaking into a Bell telephone on one wire were able to induce currents in a parallel wire sufficient to render the words audible in another telephone in its circuit. Dr Channing found this to be possible "under very favourable conditions." 48 Another striking illustration is furnished by Prof. Blake, of Brown University, U.S., who talked with a friend for some distance along a railway (using the two lines of rails for the telephonic circuit), hearing at the same time the Morse signals passing along the telegraph wires overhead. 49
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42 'Journal of the Telegraph,' N.Y., December 1, 1877. See also 'Jour. Inst. Elec. Engs.,' vol. vi. p. 523, vol. vii. p. 329; 'The Electrician,' vol. ix. p. 362.
43 'The disturbing effects of induction on ordinary telegraph wires on the same poles had long before this been noticed. See Culley's paper and the discussion thereon in the 'Jour. Inst. Elec. Engs.,' vol. iv. p. 54. See also p. 427 for Winter's interesting observations in India in 1873. As far back as 1868 Prof. Hughes, at the request of the French Telegraph Administration, undertook a series of experiments with a view of finding a remedy. The results are given in his paper read before the Inst. Elec. Engs., March 12, 1879.
44 'Journal of the Telegraph,' N.Y., October 1 and 16, and November 1, 1877. For other early observations of the same kind see 'The Telegraphic Journal,' March 1, 1878, p. 96; 'Journal of the Telegraph,' March 16, 1878; 'The Electrician,' vol. vi. pp. 207, 303.
45 'Journal of the Telegraph,' December 1, 1877, and reproduced in the 'Jour. Inst. Elec. Engs.,' vol. vi. p. 545.
46 'Electrician,' vol. i. p. 194.
47 Ibid., vol. ii. p. 182.
48 For a curiously similar case, the result of a wrong connection of the line wires, see the 'Telegraphic Journal,' vol. ix. p. 68.
49 The absence of insulation in this experiment recalls the fact that a telephone line using the earth for the return circuit often works better when the insulation is defective, as it is then less affected by extraneous currents. Thus, in 1882, the Evansville (Ind.) Telephone Exchange Company worked 400 miles of line without insulators of any kind (the wires being simply attached to the poles), and generally with better results than when insulators were used. ('Electrician,' vol. ix. p. 481.)
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