SECT. ii. ON ELECTRIC DISCHARGES. 87 



depth to which the terminal wires of the circuit were 

 plunged into the water, the resistance could be regulated 

 at pleasure, and it was immaterial in what part of the 

 circuit the vacuum tube was introduced provided the 

 circuit was completed. 



The first experiments were made with a carbonic acid 

 vacuum tube 20 inches long and 4 inches in diameter. 

 The negative terminal at one extremity of the tube was 

 of aluminium, cup-shaped, about 3 inches in diameter ; 

 the positive terminal was a wire of the same metal fused 

 into the other extremity of the tube ; the point of the 

 wire and cup were about four inches and a half apart. 

 With this tube and 2,240 cells of the battery the dis- 

 charge when the resistance was introduced had the 

 appearance of a positive and negative discharge, im- 

 pinging on and intermingling with each other, without 

 any dark space intervening. Around the negative ter- 

 minal the luminosity extends to the sides of the tube 

 and tapers to the point of the positive wire. The light 

 round the negative terminal becomes brighter, a dark 

 space appears next to it when the resistance is diminished, 

 and increases as the resistance decreases, by the rolling 

 back of the light in bright clouds to the point of the 

 positive terminal. These changes can be perfectly regu- 

 lated by the resistance, and various luminous phenomena 

 occur at each stage. 



With 2,240 cells distinct sounds were heard in the 

 tube ; with the whole battery of 3,360 series the sounds 

 were not heard till a magnet was applied to the strise, 

 when they again became audible and the striae were 

 spread over the surface of the tube. 



A carbonic acid vacuum tube with platinum terminals 

 fused into the same side far apart was now put into the 

 circuit, the part of the wires that penetrated within the 

 tube being coated with glass up to the carbon balls in 

 which they terminated. When a discharge from all the 



