AEPINUS ATOMIZBD. 



Ml 



electric properties of matter; attractions and repulsions producecl by 

 rubbed amber. Two idéal solids consisting of assemblages of monelec- 

 trionic atoms of largelj différent sizes would certainly, when pressed 

 and rubbed together and separated, show the properties of oppositely 

 electrinecl bodies; and the preponderence of the electrionic quality 

 would be in the assemblage of which the atoms are the smaller. Assu- 

 ming as we do that the electricity of the electrions is of the résinons 

 kind, we say that after pressing and rubbing together and separating 

 the two assemblages, the assemblage of the smaller atoms is resinously 

 electrified and the assemblage of the larger atoms is vitreously electri- 

 fied. This is probably the true explanation of the old-known fact that 

 ground glass is résinons relatively to polished glass. The process of 

 polishing might be expected to smooth down the smaller atoms, and to 

 leave the larger atoms more effective in the surface. 



§ 12. It probably contains also the principle of the explanation of 

 Eiiskine Murray's *) expérimental discovery that surfaces of metals, 

 well cleaned by rubbing with glass-paper or emery-paper, become more 

 positive or less négative in the Yolta contact electricity scale by being 

 burnished with a smooth round hard steel burnisher. Thus a zinc plate 

 brightened by rubbing on glass-paper rose by '23 volt by repeated 

 burnishing with a hard steel burnisher, and fell again by the same 

 différence when rubbed again with glass-paper. Copper plates showed 

 différences of about the same amount and in the same direction when 

 similarly treated. Between highly burnished zinc and emery-cleaned 

 copper, Murray found a Yolta-difference of 1*13 volts, which is, I 

 believe, considerably greater than the greatest previously found Yolta- 

 difference between pure metallic surfaces of zinc and copper. 



§ 13. To further illnstrate the tendency (§ 9) of the smaller atorn to 

 take electrions from the larger, consider two atoms; À ', of radius », 

 the greater, having an electrion in it to begin with; and A, radius <z, 

 the smaller, void. 



By idéal forces applied to the atoms while the electrion is free let 

 them approach gradually from a very great distance apart. The attrac- 



*) „On Contact Electricity of Metals'' 1 . Proc. Roy. Soc. Vol. LXIII, 1898, 

 p. 113. See also Lord Kelvin, ^Contact Electricity of Metals", Phil. Mag . 

 Vol. 16, 1898, pp. 96—98. 



