The Progress of Invention in the Nineteenth Century.

by Edward W. Byrn

““At the first condensation (of air vibrations) the hammer-shaped little wire d (G in our illustration), will be pushed back. At the succeeding rarefaction it cannot follow the return vibration of the membrane, and the current going through the little strip (of platinum) remains interrupted so long as until the membrane driven by a new condensation presses the little strip against d (the hammer G) once more. In this way each sound wave effects an opening and closing of the current.””

FIG. 56.—PROF. BELL’S TELEPHONE, MARCH 7, 1876.

Reis evidently did not know how to make the vibrations of his diaphragm translate themselves into exactly commensurate and correlated electric impulses of equal rapidity, range, and quality. If he had done this, he would have had a speaking telephone, but a make-and-break contact could never do it, and hence he in his later instruments attached to them a telegraphic key in order that the sending operator might communicate with the receiving operator. If Reis’ telephone had been a speaking telephone, this would have been unnecessary. Furthermore, it is inconceivable how the intelligent, progressive, and scientific Germans could have failed to have given to a speaking telephone in 1860 the immediate honor and attention that it deserved. In America, the Bell speaking telephone, invented in 1876, was known all over the civilized world the same year. Reis’ broken contact circuit would transmit musical tones, because musical tones vary chiefly in rapidity of vibration, rather than in range, or quality, and the chattering contacts of Reis’ telephone would transmit musical tones because said contracts could be adjusted to the practically uniform range of vibration. Prof. Bell, however, had made a special study of articulate speech, and knew that speech was not essentially musical, but was composed of an irregular and discordant medley of vowel and consonant sounds, whose vibrations varied not only in pitch or rapidity like musical tones, but also in the quality or kind of vibrations as to range and loudness. In his invention, therefore, he did not make and break the circuit as did Reis, through the contact points, but he used the more sensitive plan of a constantly closed circuit, and merely caused the current to undulate in it by a principle of magnetic induction. This principle was first discovered by Oersted, and developed into the well known fact that when a piece of iron is moved back and forth from the poles of an electro-magnet an induced current is made to oscillate in the helix of the electro-magnet. The difference between Reis’ separating make-and-break circuit, and the Bell continuous but undulating current, might be illustrated by the difference between the impulses delivered by the beating of the drum sticks on the head of a drum, on the one hand, and the alternate pulling and slackening of a kite cord, on the other. In the successive impacts on the head of a drum there could not be so sensitive a transfer of motion to the lower head of the drum as there would be transferred to the kite by the movement of the hand holding the kite cord. Reis’ plan resembled the broken drum beats, and Bell’s the kite cord, which always preserved a certain amount of tension. Bell accomplished his object by the means shown in [Figs. 56] and [57], in which [Fig. 56] represents his first patent of March 7, 1876, and [Fig. 57] his second patent of January 30, 1877. In both cases the current was a continuously closed one, and was not alternately made and broken as by the separating contacts of Reis. Prof. Bell caused the vocal air vibrations to undulate or oscillate the continuously closed circuit by the principle of magnetic induction as follows (see [Fig. 56]): He caused diaphragm a, when spoken against, to vibrate the armature c in front of the electro-magnet b, but without touching it, and as the armature approached and receded from the electro-magnet it induced an undulating but never broken current in the helix of this electro-magnet and along the line to and through the helix of the electro-magnet f at the distant receiver, and this undulating current, influencing the armature h, which touched the diaphragm i but not the electro-magnet, produced in the attractive influence of the magnet on this armature and diaphragm, vibrations of the same rapidity, range, and quality as those vocal vibrations that acted upon the first diaphragm a. In other words, the sequence of transference was air vibrations in A, mechanical vibrations of diaphragm a, electrical undulations traversing the line, induced vibrations in armature h and diaphragm i, and air vibrations again resolved back into sounds of articulate speech, the same as those spoken into A. It will be perceived that in the Bell telephone both transmitter and receiver were of identical construction. This is better shown in [Fig. 57] of his later patent, in which the horizontal line below the electro-magnet on one side represents a metal transmitting diaphragm, and the horizontal line under the electro-magnet at the other side was the receiving diaphragm. Not only were the sounds thus reproduced, but as the circuit was continuous and never broken by any separating contacts, the extreme sensitiveness of the electric vibrations set up by magnetic induction was such that the discordant and irregular quality of the vibrations of articulate speech were transferred and reproduced with exact fidelity, as well as the musical tones, and this rendered the speaking telephone a success. In later telephones the current is actually transmitted through the contacting points, but this only became practicable after the carbon microphone transmitter was invented, in which the essential undulations of the electric current were produced in another way, i. e., by the application of the important discovery that the varying of the pressure on carbon, by vibration, varied its conductivity, and in this way produced the same result of undulating a current without breaking it. This in no wise detracts from the value of the principle of the continuous undulating current discovered and employed by Prof. Bell, between which and the breaks of the hard platinum points of Reis there is a difference as wide as the difference between success and failure.

FIG. 57.—PROF. BELL’S TELEPHONE, JANUARY 30, 1877.

The form in which Prof. Bell’s telephone was placed before the public was not that shown in the patents, but it quickly assumed the well-known shape of an elongated cylinder forming a handle, with a flaring mouth-piece at one end. This development in form is credited to Dr. Channing in 1877, and it is the familiar form to-day, whose internal construction is shown in [Fig. 58]. The handle is made of hard rubber, and the cap or mouth-piece, which is screwed thereon, is also of hard rubber. The diaphragm A, of thin ferrotype plate, is clamped at its edges between the cap, or mouth-piece, and the handle. The compound magnet B is composed of four thin flat bar magnets, arranged in pairs on opposite sides of the flat end of the soft iron pole piece c at one end, and the soft iron spacing piece d at the other end, the magnets being clamped to these pieces with like poles all in one direction. The end of the pole piece c extends to within ¹⁄₁₀₀ to ²⁄₁₀₀ of an inch of the diaphragm, or as near as possible so that the diaphragm does not touch it when it vibrates. On the pole piece c is placed a wooden spool on which is wound silk-covered wire (No. 34, Am. W. G.). This wire fills the spool, and its ends are soldered to two insulated wires which pass through a flexible rubber disc f below the spool and extend respectively to the two binding posts at the opposite end of the handle. The current passes from one binding post and its connecting wire, through the wire on the spool, and thence to the other connecting wire and binding post. When used as a transmitter, vocal vibrations acting mechanically on the diaphragm A produce undulatory vibrations by magnetic induction in the spool of wire, which are transmitted to the other end of the line; and when used as a receiver, the undulatory vibrations from the remote end of the line produce mechanical vibrations in the diaphragm, which set up air vibrations that are reproductions of articulate sounds.