On the Luminous Discharge of Voltaic Batteries. 541 



The vacuum-tubes I used were prepared by means of carbonic acid 

 (Philosophical Transactions, 1859, part 1. p. 137). For the sake of 

 reference I will denote these by the original numbers which I am 

 accustomed to attach as the vacua are completed : — in the following 

 experiments these were 146, 187, 190, 196, 202, and 219. 



No. 146 is 24 inches long and 18 inches in circumference, and has 

 a copper disc 4 inches diameter at one terminal and a brass wire at 

 the other : this vessel is figured in my last communication. No. 187 

 and 196 (see fig. 1) are each about 6 inches long and 1 inch 

 diameter, with gas-coke balls \ inch diameter, attached to the 

 hermetically sealed platinum wires, the wires being protected by glass 

 tubing as far as the balls, placed inside the tube 3 inches apart. 



Fig. 1. 



No. 190 has brass wires, and No. 202 silver wires -attached to the 

 platinum : both these tubes (fig. 2) are of the same dimensions as 

 No. 187 and 196. No. 219 is 4 inches long, has gas-coke balls of 



Fig. 2. 



t J 



about |th of an inch in diameter, and 1 inch apart : the caustic 

 potash originally attached to this tube has been scaled off; the form 

 is shown in fig. 3. 



Fig. 3. 



> 



With the inductive coil the discharge in 146 exhibits a large cloud- 

 like luminosity on the plate, which in these experiments was always 

 made the negative terminal. On the positive wire, minute luminous 

 spots were visible. At intervals, apparently by some sudden energetic 

 action, flashes of bright stratified light would dart through the 

 vacuum ; but by carefully adjusting the contact breaker, the discharge 

 could be made to pass, producing a white glow on the negative plate, 

 without to the eye affording any appearance of an intermittent 

 discharge. 



In 187 and 196 the stratifications were narrow from the positive 



