ON PROFESSOR BELL S ARTICULATING TELEPHONE. Ipl 



were separate pairs of reeds or forks employed. This was the 

 practical end which Professor Bell had in view, when he com- 

 menced his researches in Electric Telephony. He soon found it 

 necessary to designate by distinct names a variety of electrical 

 currents by which sound could be produced. The three primary 

 varieties are designated. Intermittent, Pulsatory, and Undulatory. 

 The conception of this last is entirely original with Professor Bell, 

 who thus defines them ; — floe. cit. pp. 4, 5, 6.) 



An Intermittent current is characterised by the alternate 

 presence and absence of electricity upon the circuit. 



A Pulsatory current results from sudden or instantaneous 

 changes in the intensity of a continuous current. 



An Undulatory current, is a current of electricity, the intensity of 

 which varies in a manner proportional to the velocity of the 

 motion of a particle of air during the production of a sound. 



It may be remarked here, that it is the Undulatory current 

 which renders possible the transmission of articulate speech. ■ 



Currents may be 'Mirect " or '"reversed" according as the 

 electrical impulses are all of one kind, or are alternately positive 

 and negative. " Direct " currents may be still further dis- 

 tinguished as '' positive '' or "negative," according as the impulses 

 are of one kind or of the other. Hence, Telephonic currents 

 of electricity may be — 



/ (Positive I Positive Intermittent Current. 



Intermittent I^^^^^ct 



/ \ Negative 2 Negative ,, ,, 



\ Reversed 3 Reversed ,, „ 



/ I Positive 4 Positive Pulsatory Current. 



Pulsatory | ^ (Negative ^ Negative „ „ 



\ Reversed 6 Reversed „ „ 



/ Direct ( Positive 7 Positive Undulatory Current, 



Undulatory | Negative 8 Negative 



"" Reversed 9 Reversed „ „ 



W. L. C. 



