of Electricity through Hot Gases. 443 



constant. I found it impossible to do this for any length 

 of time, and so endeavoured to make the experiments as 

 quickly as possible. For this purpose a series of small storage- 

 cells were arranged within easy reach of the observer, and 

 connected in such a way that the number of cells in the 

 circuit could be altered by lifting a wire from one mercury 

 cup and putting it in another. The following are the results 

 obtained in this way with hydrochloric-acid gas at a yellow 

 heat, the observations made within a short time of each otber 

 being enclosed in brackets : — 



Number of Cells. 



Deflexion. 



Deflexion per Cell. 



3( 



35) 



3-9 -) 



13 I 



4-3 f 



if 



35 ( 



3-9 f 



13 J 



4-3 j 



5 ) 



45 S 



9-0 } 



H 



35 f 



8-75 f 



H 



20 f 



10-0 ( 



4 ) 



35J 



8-75) 



1} 



351 



20 j 



4-4 \ 

 5-0 j 



These experiments 



seem to indicate 



that these gases obey 



Ohm's law. 







Influence of the Temperature of the Electrode on the Passage 

 of Electricity through Hot Gases. 

 The condition of the electrodes exerts a most powerful 

 influence on the passage of electricity through the best 

 conducting gases. This was proved by several experiments 

 in which cold electrodes were suddenly dipped into a gas 

 maintained at a temperature sufficiently high to make it 

 conduct. This experiment was tried in three ways — first,, 

 with the platinum tube heated by the furnace ; secondly, with 

 the tube heated by the current ; and, thirdly, with the cru- 

 cible heated by the oxy-hydrogen blowpipe. In all these 

 cases an arrangement was fitted up which enabled the 

 observer to lift the electrodes (or one of them in the case of 

 the tube heated by the current) out of the hot gas, allow 

 them to cool, and then rapidly replace them. It was always 

 found that however hot the gas might be no deflexion of the 

 galvanometer occurred when the cold electrodes were first 

 placed in the hot gas, and that the time when the mirror of 

 the galvanometer began to move was just the time the elec- 

 trodes began to glow. The experiment was repeatedly tried 

 both with thick and thin platinum wires, and with thin carbon 

 filaments and thick carbon rods. The cooling of the gas by 

 contact with the electrode does not seem sufficient to explain 



