382 IDENTITY OF THE ELECTRICITIES. [SECT. xxxv. 



the various coincidences in their modes of action on which 

 their identity has been so ably and completely established 

 by that great electrician. 



The points of comparison are attraction and repulsion at 

 sensible distances, discharge from points through air, the 

 heating power, magnetic influence, chemical decomposition, 

 action on the human frame, and, lastly, the spark. 



Ordinary electricity is readily discharged from points 

 through air, but Dr. Faraday found that no sensible effect takes 

 place from a Voltaic battery consisting of 140 double plates, 

 either through air or in the exhausted receiver of an air-pump, 

 the tests of the discharge being the electrometer and chemical 

 action a circumstance owing to the small degree of tension, 

 for an enormous quantity of electricity is required to make 

 these effects sensible, and for that reason they cannot be 

 expected from the other kinds, which are much inferior in 

 degree. Common electricity passes easily through rarefied 

 and hot air, and also through flame. Dr. Faraday effected 

 chemical decomposition and a deflection of the galvanometer 

 by the transmission of Voltaic electricity through heated air, 

 and observes that these experiments are only cases of the 

 discharge which takes place through air between the char- 

 coal terminations of the poles of a powerful battery when 

 they are gradually separated after contact for the air is then 

 heated. Sir Humphry Davy mentions that, with the 

 original Voltaic apparatus at the Royal Institution, the dis- 

 charge passed through four inches of air ; that, in the ex- 

 hausted receiver of an air-pump, the electricity would strike 

 through nearly half an inch of space, and the combined effects 

 of rarefaction and heat upon the included air were such as to 

 enable it to conduct the electricity through a space of six or 

 seven inches. A Ley den j ar may be instantaneously charged 

 with Voltaic, and also with magneto electricity another 

 proof of their tension. Such effects cannot be obtained 

 from the other kinds, on account of their weakness only. 



The heating powers of ordinary and Voltaic electricity 



