, 330 



4. That this heating of the negative terminal in the discharge from 

 an induction coil had some intimate relation to the heating of the 

 positive pole of the voltaic battery was very probable ; but why in 

 the one case the heat should be evolved at the negative, and in the 

 other at the positive terminal, appeared extraordinary and well 

 worth further investigation. The result of the experiments I have 

 made with this object forms the subject of the present communication. 



5. After verifying the fact that the heating of the negative terminal 

 of an induction coil is always obtained either in a carbonic acid va- 

 cuum, in rarefied gases, or in air, provided the terminal wire is thin, 

 but not if thick, I proceeded to examine with greater precision than 

 formerly the nature and character of the luminous discharges in vacuo 

 as obtained from my water-battery, as well as from the 400 insulated 

 cells of the nitric-acid battery (Proceedings, March 15, 1860) ; and 

 for this object I had several small vacuum-tubes constructed, about 

 3 inches long and 1 inch diameter ; in each of these, two metallic or 

 carbon balls, about -J- of an inch in diameter, were attached to the pla- 

 tinum wires, hermetically sealed in the tube about one inch apart. 



Fig. 1. 



Each wire is protected by a glass tube as far as the ball ; the vacuum 

 is obtained by means of carbonic acid absorbed by caustic potassa, as 

 described in my former communications. 



6. The discharges in these tubes from an induction coil or from my 

 water-battery present nearly the same appearance, viz. a brilliant 

 luminosity surrounding the negative ball, generally without (fig. 2), 

 but sometimes with (fig. 3) a minute stratified discharge from the 

 positive. 



Fig. 2. Fig. 3. 



7. When the vacuum-tube is introduced into the circuit of 400 in- 

 sulated cells of the nitric-acid battery, the discharge at first always 



