OP ARTS AND SCIENCES. 223 



vibrating parts of the ear, we might suppose that even a small por- 

 tion of a simple sound-wave, if it produced any recognizable sensa- 

 tion, would give a sound of a pitch corresponding to the length of 

 the complete sound-wave, of which a part had impressed the ear." 



The method devised in 1884 to remedy the defect consisted of a 

 telephonic circuit containing two magneto-telephones, connected in 

 the usual manner for the transmission of sound, and a circuit-mak- 

 ing wheel. The latter was a wheel of vulcanite, furnished with a 

 single narrow conducting strip of brass extending over a small arc 

 of its circumference. Against the edge of the disk pressed a spring 

 whose end was faced with platinum. If such a wheel is revolved at 

 a uniform speed, it is clear that once in each revolution the circuit 

 between the two telephones is closed for a brief period, whose dura- 

 tion can readily be determined when the speed of the wheel and the 

 angular extent of the conducting sector are known. If now the 

 sound of a tuning-fork giving simple harmonic vibrations actuates 

 the transmitting telephone, the electrical undulation produced will 

 be a sinusoidal one, and the air-waves produced at the receiver will 

 be substantially similar in character, and continuous, provided the 

 contact-making spring rests upon the metal sector of the wheel so 

 as to complete the circuit. But if the wheel is revolved the electri- 

 cal current is broken, except during a brief interval of time when 

 the spring is in contact with the metallic sector; at which period, 

 however, a current of brief duration is sent through the line and a 

 correspondingly brief sound is produced at the receiver. Except in 

 so far as self-induction and like phenomena act to prevent this, 

 these brief electrical currents are still sinusoidal in character; 

 and hence should give rise at the receiving telephone to waves or 

 portions of a wave of sound which are sinusoidal in form, and 

 should be perceived by the ear as a simple tone. In so far as the 

 motion of the diaphragm of the receiver deviates from a simple har- 

 monic one, either from disturbing electrical effects due to self- 

 induction, or from the acoustic effect of the sudden pull and 

 L-elaxation which occur when the circuit is made and broken by the 

 contact-making spring, disturbing sounds will of course be added 

 to the simple tone, which would otherwise be the only one produced. 

 But unless the disturbing causes are excessive, the pitch of the 

 simple tone corresponding to that given by the tuning-fork actu- 

 ating the transmitter will predominate. And as a matter of fact 

 these disturbances are slight, as is shown by the fact that there is 

 no difficulty in transmitting speech through a circuit with a mag- 



