OF ARTS AND SCIENCES. 229 



but could easily be seen to be brighter when the condenser was in the 

 circuit. The following is the record of observations upon three gases, 

 and the equal air resistance, with and without a condenser : — 



1. Current passing through Geissler's tube of CO. 



With condenser, deflection = 8 cm. 

 Without „ „ =8 cm. 



With „ light increased. 



Without „ „ decreased. 



2. Current passing through Geissler's tube of H. 



With condenser, deflection = 8 cm. 

 Witliout ,, „ =8 cm. 



With „ light increased. 



Without „ „ decreased. 



3. Current passing through Geissler's tube of 0. 



With condenser, deflection = 8 cm. 

 Without „ „ = 8 cm. 



AVith „ light increased. 



Without „ ,, decreased. 



4. Current passmg through air resistance equal to the resistance of Geissler's 

 tube. 



With condenser, deflection == 8 cm. 

 Without „ „ = 26 era. 



With „ light increased. 

 Without „ „ decreased. 



Let C, be the condenser ; ^S*, the entire energy of current which would 



produce magnetic effect ; L, that part of the energy expended in light ; 



and m, the deflection of the galvanometer. We shall then have in 



air : — 



Without C, S — L =(p (m) 

 With C, 5 — Li = (/) (m^) 



m = 3.25 times jn^ 



L <L^ 



m gas 



Without C, 5 — ^2 = </) (wj) 

 With C, S^L3 = (j> (wg) 



TO2 — Wig 



In other terms, having an air resistance equal to that of the Geissler's 

 tube, the introduction of a condenser increased the light, and decreased 

 the deflection of the galvanometer. Or replacing the air resistance with 



