On the Atomic Theory. 85 



llie best conductors of electricity, as a sufficient quantity of their 

 caloric is easily removed on its passage through them ; but a 

 dead animal completely cold becomes a bad conductor. All the 

 dry metallic oxides are non-conductors, as their calorific atmo- 

 spheres are small and of course strongly attached to their atoms. 

 Glass also, which consists of different oxides fused into one solid 

 mass, is a non-conductor on the same principle. Yet glass be- 

 comes a good conductor when sufficiently heated so as to enlarge- 

 its calorific atmospheres, like dead animals while they retain a 

 remnant of their vital heat*. 



The electric fluid moves with great velocity through metallic 

 bodies and charcoal, while the progress of caloric in those sub- 

 stances is comparatively very slow, and light is completely ob- 

 structed by them. Light, on tiie other hand, passes with ease 

 ■ through glass, mountain crystal and calcareous spar, and other 

 diaphanous bodies ; whereas, they in a great measure prevent 

 the passage of caloric and electricity. Hence it should appear 

 that caloric, electricity and light are substances, and simple sub- 

 stances, totally different from each other. 



When the electric fluid is made to pass in a perfect vacuum 

 no light or heat is produced, because this element does not pos- 

 sess those properties in its puie or simple state f. 



When a strong electric spark is passed in atmospheric air sr 

 in any gas, a flash of light is produced. This is occasioned by 

 the liberation of a portion of the specific heat, which resumes its 

 former station again, round the particles of the air, the instant 

 the influence of the electric matter, which is very rapid and in- 

 stantaneous, terminates. The same effect is produced on the 

 large scale of nature: — instance; — thunder and lightning. 



* Dr. Thomson, as usual, misrepresented my meaning on this subject, 

 page 60 of his Annals for July 1814. His remarks are as follow : " If this 

 hypothesis were correct, the metals ought to be non-conductors, for they 

 Ijave little specific heat ; and water and hydrogen ought to be the best con- 

 ductors in nature, as they have the highest specific heats." I do not agree 

 with the Doctor in his position.s : metals contain a prodigious quantity of 

 specific heat, and that heat is not so intimately united as that of water, ex- 

 cept the small portion which is necessary to the fluidity of the latter ; and 

 when it is deprived of this portion and becomes ice, it is no longer a con- 

 ductor. In this respect it agrees with glass. Hydrogen contains a consi- 

 derable quantity of specific heat, but much less than chemists suppose; yet 

 it retains it v.-ith greater force than the metals, and consequently is not so 

 good a conductor. I now come to the point in which the Doctor attempts 

 to pervert my hypothesis. He insinuates that I meant that those substances 

 V'liich contain the greatest quantity of specific heat are the best conduct ous; 

 — no per.-ion but the Doctor himself could draw such an inierence. I founded 

 my hypothesis on the force of union of caloric to bodies, and not on the quan- 

 tity which they contain ; and substances which contain least of it round 

 their ])ai tides or atoms, retain it, most frequently, with tiie greatest force, 

 t See mv Bsssiy on the Atomic Theory, and Electrical Phicnomena. 



F 3 The 



