﻿5G2 Mr. Carl Barus on Telephonic 



the economic disposition of the wire relative to resistance, 

 and in the strong field of induction normally through the 

 diaphragms even when the magnet A is not remarkably strong. 

 The chief condition of sensitiveness is close approach of the 

 coil ends of the armature to the two walls of the sound- 

 chamber, respectively. Hence this adjustment must be made 

 with care and the diaphragms must not buckle. I usually 

 placed armature and diaphragm in actual contact on one side 

 and all but in contact on the other, and then tapped the 

 sound-chamber into position. 



Among other devices for increasing the sensitiveness of the 

 telephone I may mention the endeavour to follow the excur- 

 sions of the Bell diaphragm by a microphonic contact*. My 

 best results were obtained by soldering a platinum stylus 

 axial! y to the centre of the diaphragm. The end of the stylus 

 just touched a little pellicle of carbon suspended by a delicate 

 spring, the arrangement being in circuit with four Leclanche 

 cells and a second telephone. With this relay apparatus 

 sounds above a certain intensity were greatly increased, 

 while sounds of lower intensity were either left unchanged or 

 even extinguished, and the degree of sensitiveness varied too 

 rapidly for convenience or certainty of measurement. Simi- 

 larly ineffectual efforts were made in adapting transformers 

 and condensers for the purpose. 



4. Results. — The current i f passing through the telephone 

 during the time of contact, considered apart from self- 

 induction f ; may be expressed under the form 



V- 



e 

 EE 



r 

 R + r 







r ' 



(1) 



where / is the resistance of the shunt containing the tele- 

 phone and the electromotive force e, R the resistance of the 

 shunt containing the electromotive force E, and r the resist- 

 ance of the remaining branch circuit. If, therefore, by any 

 independent means the ratio tf/E has been found, equation (1) 

 is available for computing i' . The necessary data are obtain- 

 able without auxiliary measurements of e/E by taking advan- 

 tage of both margins of the interval of silence already alluded 

 to in § 1, in the way presently to be shown. 



In the following table I shall therefore, in addition to the 



* Somewhat similar experiments were made by Messrs. Thomson and 

 Houston ; also by Hughes and others, 

 t Tested by the blunt-toothed key (§ 3) and found admissible. 



