452 On a new Relation between Heat and Static Electricity. 



if a small sphere of glass have two platinum electrodes fused 

 into the two sides and it be gradually heated, the galvanometer 

 does not move for some time ; but after the first movement is 

 observed, the needle quickly passes up to 90°. 



If we assume that hot air possesses the power of carrying 

 off 4- electricity more readily than — , the whole of Dr. Guthrie's 

 apparently contradictory experiments of the different effects of 

 + and — electricity may be easily explained. Thus a heated 

 body cannot be charged with + electricity, because the heated 

 air carries it off. A body near a heated conductor cannot be 

 charged with — , because it induces + electricity in the heated 

 body ; this electrifies the heated air, and the electricity is then 

 carried to the electrified — body and neutralizes it. 



Faraday proved that air at ordinary temperatures carried off 

 — electricity most easily. 



Hence the experiments of Faraday, Dr. Guthrie, and myself, 

 taken in conjunction, prove the two following principles : — 



1st. That at low temperatures — electricity is taken away 

 by air most easily; at certain temperatures both electricities 

 are carried off with equal facility, and at high temperatures -f 

 electricity most easily. 



2nd. That high-tension electricity can be conveyed away at 

 low temperatures ; and as the tension gets lower and lower, it 

 requires the air to be of higher and higher temperatures to carry 

 it off. 



To illustrate the second principle, I placed a needle on the 

 knob of a fully charged Peltier's electrometer and left the point 

 within y^-g- of an inch of an earth-connected brass ball ; after 

 two hours the electroscope had only lost half a degree j and on 

 passing a current of hot air, or putting a heated point near it, 

 the electricity was instantly discharged. 



The lengthening of the electric arc after the current is once 

 established may be due to these principles, especially from the 

 well-known fact that the part of the -f carbon where -induc- 

 tion is strongest wears away most rapidly ; while the slight wear 

 of the other carbon is as much down the sides as at the point, 

 and hence it remains pointed. It is further confirmed by the 

 fact that if the electric current pass between two electrodes of 

 different oxiduable metals, the space about the light becomes 

 filled with particles of the oxide of the + pole. 



