On Induction in Telephonic Circuits. 



353 



circuit, and from the tertiary to the quaternary, were wound 

 separately, and consisted of a smaller length of wire than the 

 two which were wound side by side to form the double helix 

 used to transfer the induction from the primary to the secondary 

 circuit. 



The pitch of the sound, however, is found to be the same 

 in all the four circuits. Now, if the rate of the pulsations of 

 induced currents is greater as the order of the current is 

 higher, and if the telephone is capable of vibrating in unison 

 with these pulsations, it follows that the pitch of the sound 

 should be higher in some of the telephones than it is in others. 

 But as the pitch of the sound is the same in all, either the 

 telephones do not vibrate in unison with the rapid pulsations 

 of the currents of high order, or the sameness of pitch must 

 be due to some other cause. 



The arrangement of apparatus in the next experiment is 

 shown in tiff. 1. 



Fig. 1. 



There are three separate circuits. The primary includes a 

 battery B, a telephone T, a flat coil C, and a microphone M ; 

 the secondary includes a flat coil (7, a telephone T', and one of 

 the wires of the double helix H ; the tertiary includes the 

 other wire of the double helix and a contact-key K. L is a 

 condenser. 



The coils C and C are placed with their faces in contact 

 and their axes coincident; and the microphone is actuated by 

 a watch. 



When a battery-current circulates in the primary circuit 

 under these circumstances, currents are induced in the 

 secondary and tertiary circuits, and it is observed, when the 

 ear is applied to the telephone in the secondary circuit, that 

 the loudness of the sound is increased when the key is depressed 

 and the tertiary circuit is closed, and that it again becomes 

 weak when the key is raised and the tertiary circuit is opened. 

 The increase in the loudness is most readily observed when 

 the sound is rather faint when the tertiary circuit is open ; for 

 if the sound is already loud the increase is not so marked. 



