Fig. 12.
Fig. 13.
Eighth Form.—Lever Form.
Fig. 14.
The Transmitter described with so much minuteness by Inspector von Legat in his Report on Reis’s Telephone in 1862 (see p. 70), differs from the earliest and latest forms, so much so that some have doubted whether this form was really invented by Reis. It is not described anywhere else than in Legat’s Report (in the “Zeitschrift” of the Austro-German Telegraph Union, reprinted also in Dingler’s Journal), except in Kuhn’s Handbook, where, however, the description is taken from Legat. Nevertheless a comparison of this instrument (Fig. 14) with the original model of the ear, from which Reis started, will show that it embodies no new point. There is, first, a conical tube to receive the sound, closed at its end with a tympanum of membrane. There is next a curved lever, c d, the lower end of which rests against the centre of the membrane. Thirdly, there is a vertical spring, g, which makes contact lightly against the upper end of the curved lever. Lastly, there is an adjusting screw. It may be further pointed out that in each case the current enters (or leaves, as the case may be) the lever at its middle point. This form of transmitter is so closely allied indeed to the primitive “ear” as to be alike in every feature save the external form of the sound-gathering funnel. The only reasonable doubt is not whether it be, as Legat asserts, Reis’s transmitter, but whether it ought not in chronological order to rank second. Legat’s paper was not published, however, till 1862, whilst the fourth form was described by Reis in 1861. No trace of any instrument corresponding in form to Fig. 14, save modern reproductions from Legat’s drawing, has been found. The instrument held by Reis in his hand in the photograph (Fig. 12) is so strikingly like the form described by Legat, that it furnishes an additional reason for accepting Legat’s statement that this transmitter really is Reis’s invention.
Fig. 15.
Fig. 16.
Ninth Form.—Transitional Form.
Our knowledge of this form is derived solely from information and sketches supplied by Mr. E. Horkheimer, who assisted Reis in its construction. Figs. 15 and 16 are engraved after Mr. Horkheimer’s sketches. The conical mouthpiece was of wood: the contact pieces of platinum. The point c was attached to a springy slip of brass, g, fixed across the wooden box; and the adjusting-screw, h, served to regulate the degree of initial pressure at the point of contact which controlled the current.
Tenth Form.—The Square Box.
Fig. 17.
Fig. 18.
The last form of Reis’s Transmitter is that which has become best known, being the only one (except Fig. 9) which found its way into the market. It is here named, for the sake of distinction, as the “Square Box” pattern. It consisted of a square wooden box, having a hinged lid. Fig. 17 is reproduced from Reis’s “Prospectus” (see page 85), whilst Fig. 18 is taken from Prof. Schenk’s biographical pamphlet.
In this instrument the idea of the human ear is still carried out. The tin funnel, with its flaring embouchure, still represents the auditory tube and pinna. The tympanum, no longer at the very end of the tube, is strained across a circular aperture in the lid. Upon it rests the strip of platinum foil which serves as an electrode, and resting in loose contact with this lies the little angular piece of metal which Reis called the “Hämmerchen.” Above all lay a circular glass disk (a cover to keep out the dust), which was removed when the instrument was used. So sensitive did this form prove itself that it was found unnecessary to speak right into the mouthpiece, and the speaker in practice talked or sang with his mouth at some little distance vertically above the instrument; a method which had the advantage of not so soon relaxing the membrane by the moisture of the breath. The figures show also the auxiliary apparatus attached at the side, consisting of a key for interrupting the circuit (added at first to enable the experimenters to single out the “galvanic tones” from the reproduced tones, and later applied, as Reis explains in his “Prospectus,” on page 87), and an electro-magnet to serve as a “call,” by which the listener at the other end could signal back to the transmitter.
This form of instrument, which has been so frequently described in the Text-books of Physics, was constructed for sale first by Albert of Frankfort, later by Ladd of London, König of Paris, and Hauck of Vienna. Further details concerning it will be found in this book, in Reis’s “Prospectus,” and in other contemporary documents.
Although this form is the one most commonly referred to as “the Reis Telephone,” it is evident from a consideration of the entire group of forms that Reis’s invention was in no way limited to one individual pattern of instrument. For in all these forms there was embodied one all-embracing principle;—that of controlling the electric current by the voice working upon a point of imperfect contact, by the agency of a tympanum, thereby opening or closing the circuit to a greater or less degree, and so regulating the flow of the current.
B.—Reis’s Receivers.
First Form.—The Violin Receiver.
Fig. 19.
The first form of apparatus used by Reis for receiving the currents from the transmitter, and for reproducing audibly that which had been spoken or sung, consisted of a steel knitting-needle, round which was wound a spiral coil of silk-covered copper-wire. This wire, as Reis explains in his lecture “On Telephony,” was magnetised in varying degrees by the successive currents, and when thus rapidly magnetised and demagnetised, emitted tones depending upon the frequency, strength, etc., of the currents which flowed round it. It was soon found that the sounds it emitted required to be strengthened by the addition of a sounding-box, or resonant-case. This was in the first instance attained by placing the needle upon