that occur in the Telephone. 35 



that which results from the value of P according to the general 

 law of induction : 



T^P 



E = — — = ^B m . 27r?im . cos (2irnmt). 

 at 



The current occasioned in the telephone is proportional to this 

 quantity ; and so is the outbending of the excited membrane 

 in the receiving telephone. If the air-vibrations which excite 

 the telephone have the form 2A m . sin (27rmt), the vibrations 

 excited in the air by the telephone take the form 



2Aj„ . 2imm . cos (jZirnrnt). 



Thus the tone (Klangfarbe) of the sonorous motion, is neces- 

 sarily altered during its telephonic transit: the partial tones of 

 a higher number of vibrations come out stronger than those of 

 a smaller number. At the same time there is a phase-dis- 



placement to the amount of -x ■ 



M. Hermann has shown, in his "Telephonic Notices"*, 

 and in his last experiments, communicated to this Society, 

 that these consequences of the theory of Dubois-Reymond are 

 not verified by experience. Hermann instituted the follow- 

 ing experiments : — 



I. In the circuit of a telephone one of a pair of coils was 

 inserted, and in that of a second telephone the other coil, pa- 

 rallel with the former. All the words and letters which were 

 spoken into the first telephone could be heard distinctly out 

 of the second. The same result still followed when a second, 

 third, fourth pair of coils were in like manner inserted between 

 the two telephones. From this M. Hermann infers that the 

 induction is without any traceable influence upon the ratio of 

 intensity of the partial tones of a sound ; while, according to 

 M. Dubois-Reyinond's theory, in these cases of multiplied 

 induction a very considerable alteration in the tone must have 

 occurred. 



II. In an induction-coil oscillating currents, I, were excited 

 by a vibrating magnetic tuning-fork placed near it. These 

 currents were conducted to a telephone. In the circuit of the 

 currents I one set of windings of a double-wound electro- 

 magnet-coil of fine wire was inserted. The currents I : , induced 

 in the second set of turns of the coil, were also, a commutator 

 and key being inserted, conducted to the telephone. Moreover 

 the telephone could at pleasure be taken out of the circuit of 



* Pliiger's Archivfiir Physiologie, vol. xvi. pp. 264 & 314. 



D2 



