Fig. 45.
The last of the ten sketches of [Fig. 45] is taken from Edison’s first American Patent specification [No. 203,014, filed July 20, 1877], and shows a duplicated interrupter with springs and adjusting-screws combined with a tympanum. Further comment on this arrangement is needless, save to remark that in this patent for “speaking telegraphs,” Edison himself describes the contact-apparatus which Reis termed an “interrupter,” as a “circuit-closer,” or in another place as “circuit-breaking connections,” and, in his British Patent quoted above, as a “tension-regulator.” It is evident that if Reis could transmit speech by an interrupter which closed and opened the circuit (always in proportion to the vibrations) there is no reason why Edison seventeen years afterwards should not accomplish the same result by a similar means. But it has lately been fashionable to deny that any such device as an interrupter mounted on springs can transmit speech at all!
We have now compared with Reis’s transmitters several of the more modern inventions. It would be possible to carry comparison further were that course needed. We have not thought it worth while to rake up Edison’s now discarded lamp-black button transmitter; and we have not yet spoken of Crossley’s transmitter nor of Theiler’s transmitter, nor of their parent the Hughes’ microphone, nor of dozens of other forms. In some of these there is no specific “tympanum,” but only a sounding-board of pine-wood, and in most of them the points of loose-contact, where interruption more or less complete may occur, are multiplied. But they all come back in the end to Reis’s fundamental idea, namely that of setting the voice to vary the degree of contact in a mechanism which he called an interruptor, and which others have called a current-regulator (or, less correctly, a tension-regulator) which, because the degree of contact between its parts was varied, caused those parts to offer more or less resistance to the flow of the current, and thereby threw it into vibrations corresponding to those of the sound-wave impressed upon the tympanum. There is not a practical transmitter used in any of the telephone exchanges of Great Britain to-day that does not embody this principle.
Reis did, indeed, penetrate to the very heart the principles necessary to be observed in a successful telephone. He was master of the situation. For, as in every practical transmitter in use to-day, so in his transmitter, there was a loose contact in the circuit so arranged that the voice could act upon it, and thereby regulate the strength of the current. If you eliminate this part of the apparatus,—screw up the loose-contacts of your transmitters, so that your voices cannot affect them,—what will your telephones be worth? No: the essential principle of the transmitter—“Das Telephon” emphatically as its inventor styled it—is variable contact; and that all-essential principle was invented and applied for the purpose of transmitting speech by Philipp Reis in 1861.
If this does not suffice as a claim for the invention of the Telephone transmitter, it may well be wondered what will. We can dispense with all other features save this one. We can even dispense with the tympanum or diaphragm which Reis introduced, and can operate on the contact-parts without the intervention of this part of the combination. We can use the very metals which Reis used, and dispense with lamp-black and all the fallacious rubbish that has been subsequently devised about semi-conductors, whatever that term may mean. We can even dispense with springs and adjusting screws. But with the principle of variable contact we can not dispense. That which alone is indispensable Philipp Reis discovered.
APPENDIX II.
On the Variation of Electric Resistance at a Point of Imperfect Contact in a Circuit.
Ever since electricians had experimented with voltaic currents, and especially since the introduction of the electric telegraph, it had been a familiar fact that a loose or imperfect contact in the circuit caused a resistance to the flow of the current and interrupted it more or less completely. To obviate the occurrence of loose or imperfect contacts, binding-screws were invented; and many were the precautions taken to make tight contacts at joints in the line, the resistance of which it was desirable to maintain at a minimum. Young telegraphists were particularly instructed to press their keys well down in signalling, because a light contact would offer some resistance which, on an increase of pressure, would disappear. In fact, it was generally well known that the resistance of two pieces of metal or other conducting material in contact with one another might be made to vary by varying the goodness or badness of the contact with the application of more or less force. This fact was known to apply to good conductors, such as copper and other metals, and it was known to apply also to non-metallic conductors, such as plumbago. Plumbago points were used by Varley for the contacts of relays; it having been found that points of platinum were liable to become fused together with the passage of the current, and by so sticking rendered the instrument useless. Since plumbago was known to be infusible, it was hoped that a plumbago contact would prove more reliable. In practice, however, the plumbago relay did not turn out so well. True it did not fuse, or stick, or rust; but it was even more liable than platinum to form imperfect contacts, the resistance of the light contact being so high that a sufficient current did not pass. It is not known whether other non-metallic substances were tried; probably not, because of non-metallic substances plumbago is one of the few that are good conductors.