Electricity. 425

common fire, in a long glass tube her-metically sealed, presently became green, andafterwards yellow.

SECTION XXXVIII.

Experiments in EleBricity.

T HAT conduBing power, with respectto electricity, depends upon the vari-able state of substances, is evident from avariety of experiments. Thus glass, whichwhen cold is a perfect nonconductor, is acomplete conductor in a great degree ofheat. So also, by a contrary process, ice,which when formed in a moderate degreeof cold is a conductor, very much likewater, becomes, as Mr. Achard has dis-covered, a nonconductor in a greater degreeof cold. And I had found that though drywood, and even charcoal, made with the leastpossible degree of heat, is a nonconductor*yet when it has been exposed to more heat,it is the most perfect of all conductors, notexceeded even by the most perfect metals

themselves.