386 Correspondence of J. Nickles. 
alone? Some physicists may think so. For ourselves, we be- 
lieve that the reduction is due to the volatilised carbon ; for it is 
well known that the luminous arc is never produced without a 
transfer of material, and the material transferred in this case is 
nothing else but incandescent carbon. 
earth’s magnetism. But if a pistol containing a lead ball is fired 
origin of the earth’s magnetism.* Once magnetised, it induces 
magnetism in the steel spring, acting thus like an ordinary mag- 
net. By mterposing a screen between the spring and the line of 
verify, I will take this opportunity to correct an opinion too wr 
XV, 
par 
trials; I hope soon to establish the contrary and without having - 
* This Journal, January, 1854, xvii, 116. 
