DISCHARGE OF ELECTRICITY FROM HOT PLATINUM. 
253 
Fig. 2 shows the way in which the leak from the hot wire varies with the P.D. at 
pressures of 766, 211, and 27 millims. of mercury, the wire being negatively charged. 
When the P.D. is small, the current is nearly independent of the P.D., but with 
larger P.D.’s the current rises rapidly with the P.D., the rate of, rise being greater 
the lower the pressure. The temperature of the wire in this case was 1648° C., and 
the wire was 13 centims. long and OH millim. in diameter. 
Fio". 3 shows the variation of the negative leak with the P.D. at pressures of 
0-0036, 0-18, 0-29, 0’49, 0-81, and 12-1 millim.s. of mercury. At these pressures the 
rise of current with the P.D. is more rapid the higher the pressure. The tempeiatuie 
of the wire in this case was 1483° C. 
Fig. 4 shows the variation of the negative leak with the pressure, using constant 
P.D.’s of 250 and 40 volts. With 40 volts the current is quite independent of the 
