298 Drs. W. De La Rue and H. W. Miiller. [June 14, 



terminals themselves to the passage of a discharge from gas to 

 terminal and terminal to gas. 



It is shown that, at moderate exhausts, the resistance to the passage 

 of the discharge is uniform along the length of the column of gas, 

 and that at high exhausts it is not so, and that the total resistance 

 increases but slightly with an additional length of the column ; more- 

 over, that, at these low pressures, the main impediment is in the 

 passage of electricity between gas and terminal or terminal and gas ; 

 this is much greater at the negative than at the positive terminal. 



The authors have next studied the electrical condition of a gas in 

 the immediate vicinity of the negative terminal. In order to do this 

 they constructed a tube 4J inches (11*4 centims.) long and 1J inches 

 (4*8 centims.) diameter. One terminal is in the form of a point, the 

 other in the form of a ring. The positive pole of the battery was con- 

 nected with the point and the negative either to the ring alone or to 

 earth as well ; the ring terminal of the tube was, when the battery 

 was insulated, connected with earth either by means of a stout wire 

 or 3 feet (91*4 centims.) of fine platinum wire, 0*002 inch (0*005 

 centim.) diameter, and offering a resistance of 81 ohms, or a moistened 

 cork offering a resistance of 4,300,000 ohms. In the tube were sealed 

 three idle wires, 1, 2, 3, covered with the exception of their extremi- 

 ties with fine glass tubing (fig. 10). No. 1 idle wire is 0*002 inch 



Fig. 10. 



■(0-005 centim.) ; No. 2 0*2 inch (0*5 centim.) ; and No. 3 0*6 inch 

 (1*5 centims.) from the ring. The ring terminal, when connected 

 to earth, was found to be always at zero potential ; notwithstanding 

 this there was frequently observed, more especially as the exhaust 

 was increased, a negative potential when the idle wires were con- 

 nected successively with the electrometer, amounting in one case with 

 an air charge, pressure 0*01 millim., at wire No. 2, to 1,068 cells, at 

 wires 1 and 3 to 912 cells. At other times a plus potential was 

 observed. Many experiments were made to determine the precise 

 conditions which developed a negative potential or a positive potential, 

 but unsuccessfully, and it was inferred that this depended on the 



