10 



PROCEEDINGS OF THE AMERICAN ACADEMY 



represented by a sinusoidal curve, or by the resultant of several sinus- 

 oidal curves. 



Intermittent, pulsatory, and undulatory currents may be of two 

 kinds, — voltaic, or induced; and these varieties may be still further 

 discriminated into direct and reversed currents ; or those in which 

 the electrical impulses are all positive or negative, and those in which 

 they are alternately positive and negative. 



I 00 



( 



^ s 



CD in 





H ^ 



Intermittent. 



( Voltaic. 

 (^ Induced. 



{ 



( Reversed (See par. 8). 



Direct (See par. 1, 2, 3, 4, 5, 6). 



Reversed. 



Direct. 



a 



_ r^ •— ' 



.--^Pulsatory- 



\ 



Voltaic, 





Undulatory. 



\ 



( Direct (See par. 9). 

 ( Reversed. 



/ Induced. < r, ' j 

 ^ I Reversed. 



ect (See par. 11, 12, 13, 15). 



versed. 

 Direct. 

 Reversed (See par. 10). 



Voltaic. 



Induced. 



( Direc 

 ( Reve 



{ 



17. In conclusion, I would say that the different kinds of currents 

 described above may be studied optically by means of Konig's mano- 

 metric capsule.* The instrument, as I have employed it, consists 

 simjily of a gas-chamber closed by a membrane to which is attached 

 a piece of clock-spring. When the spring is subjected to the attraction 

 of an electro-magnet, through the coils of which a "telephonic " current 

 of electricity is passed, the flame is thrown into vibration. 



I find the instrument invaluable as a rheometer, for an ordinary 

 galvanometer is of little or no use when " telephonic " currents are to 

 be tested. For instance, the galvanometer needle is insensitive to the 

 most powerful undulatory current when the impulses are reversed, and 

 is only slightly deflected when they are direct. The manometric cap- 

 sule, on the other hand, affords a means of testing the amplitude of 

 the electrical undulations; that is, of deciding the difference between 

 the maximum and minimum intensity of the current. 



* Konig. " Upon Manometric Flames," Phil. Mag., 1873, XLV., No. 297, 

 298. 



