[WILSON] CURRENT FROM HOT PLATINUM IN AIR 55 
From this curve we get B — 0-5 E.S. units, so that 0-436 p, =0-5 
or 9, — 1-15. Also A= 10% = 0-146/k p,, which gives k = 43 cms, 
per sec. for one volt per cm. Below 200 volts the disturbance of the 
electric field by the ions present is too large for the theory given, to be 
applicable. 
ê 
Current. (1=1:7 x10 ampere.) 
5 
200 
(Outer tube negative. : 10.) 
oO 100 200 300 400 Cells. 
(= 800 Volts.) 
/00 
The velocity of an ion, in air at atmospheric pressure and 1,080° C., 
supposing it to consist of a single molecule comes out on the ordinary 
kinetic theory to be about 67 cms. per sec., which agrees very well 
with the value just found, so that we may conclude that the positive 
ions emitted by the hot platinum are single molecules of the gases 
present. 
The curve with the inside electrode positive can also be represented 
by V = AC + B between 20 and 100 volts, but B is too small to be 
estimated accurately. 
The current at the inside electrode when it is positive is equal to 
2mrr,0,kF,. The relation between F and the current density i was given 
by Sir J. J. Thomson,* but has not so far been tested by comparison 
with experimental results. 
* “Conduction of Electricity through Gases,” p. 208. 
