rent-regulator, identical with the combination used by Reis. Too loud shouting in either the Reis or Blake transmitters spoils the articulation by breaking the circuit.
Reis's transmitters have been called make- and break-circuit instruments. If so, the Berliner and Blake transmitters, operating on the same principle, are also make- and break-circuit instruments. If, on the other hand, the Berliner and Blake transmitters, by their current-regulators, determine undulatory electric currents, in correspondence with the sound-waves, the Reis transmitters, by the same mechanism, necessarily do the same.
The identity of the mechanism of the current-regulators in four of Reis's transmitters with the mechanism in six modern forms of transmitter is strikingly exhibited by Professor Thompson in a comparative plate.
In connection with the Reis current-regulator, now in almost universal use, it has been in later times found generally advisable to use an induction-coil. It is an interesting fact in the evolution of the telephone, though it may not be stated in the book before us, that Ferguson's chemistry, published in 1868, states that Dr. Wright in England used a Reis transmitter in the primary circuit of an induction-coil. The combination of current-regulator and induction-coil in the modern transmitters is therefore old.
In the third section of the appendix, Reis's receivers are compared with recent instruments. The examination in this case, also, is much aided by a comparative plate. Reis's electro-magnetic receiver is shown to combine the three following essential elements, which enter into the Yeates, Gray, Bell, Edison, and other receivers: 1. An armature acted on by an electro-magnet; 2. An armature elastically mounted; 3. An armature of sufficiently extended surface to set in motion aerial sound-waves. This discussion has been anticipated in previous pages. Professor Thompson, in summing up his close analysis, points to Reis as the genius by whom the essential principles of all the electro-magnetic receivers now in use were discovered and combined so as to reproduce articulate speech.
A section in the appendix is devoted to the "undulatory" current in Reis's telephone. We have already seen that the function of the Reis transmitter was to vary the strength of the electric current, and not to break it. Reis was accustomed to speak of opening and closing the circuit in describing these instruments, not in the technical sense of modern telegraphy, nor with the idea of sending intermittent signals, but in the sense of increasing or diminishing the current, without going so far as absolutely to break it. This is abundantly proved by the context in his descriptions, and by the operation of his instruments. He states, in his first memoir, that, to reproduce any sound, or combination of sounds, all that is necessary is to set up in the receiver vibrations whose curves are identical with those of the