IMPARTED TO A VACUUM BY HOT CONDUCTORS. 
517 
themselves. From the constant A we o1)tain the nmnher n of free corpuscles in a 
' A. A is 
obtained by |)utting corresponding values of 6 and C in the equation 
logic ^ = logio C — logqo 9 — logio ‘788 + 9-523 + (2-24 X 10+) 0“+. 
At 6 (ah.solute) = 1542° this gives A = 1-51 X 10"®. The various constants in the 
logarithmic equation come from the area of the wire, which was -394 sq. centim., and 
the value of the charge on an ion, which was 
taken to be 6 X 10~+® electrostatic unit. 
The value of ?n/Il (m being the mass of, and 
Pt the gas-constant for, one corpuscle) was 
found to be = 1-204 X 10“+f Putting this 
in the expression for n, we find 1-3 X 10^+ 
free negative ions in a cubic centimetre of 
platinum at 1542° absolute. An independent 
value of n lias been obtained by Mr. Patter¬ 
son* from experiments on the change of 
resistance of platinum in a magnetic field. 
This when calculated liy the metliod given by 
Professor Thomson t yields ii = 1-37 X lO". 
The agreement of tlie value found above with 
this is really very good, when one considers 
the numerous sources of error to which the 
measurements are liable, and that an error of 7 per cent, in the absolute temperature, 
among other things, would multiply the value of n by ten. 
It was thought that possibly some regular change in the value of n with the 
temperature might be found if values were calculated for difierent temperatures. It 
was found, however, that n oscillated in an irregular manner between -43 X 10^+ and 
2-0 X 10”+, so that the experiments yielded no evidence of any detectable variation 
of n. This method of olfiaining n is extremely inaccurate, so that tlie agreement 
between tlie above numbers is really better than would be expected. 
The signification of the constant h = 4)/Il which occurs in the exponential factor is 
equally important, since ffi is the work done Ijy an ion in passing through the surface 
layer. We obtain h from the equation 
cubic centimetre of solid platinum, since we have the relati 
on n = 
ZniTT 
Ii 
h 
log. cyc' 
where C, C' and 0, 6' are corresjionding currents and absolute temperatures. 
‘ Phil. Mag.’ (G), vol. .3, p. 643. 
t J. J. Thom.sox, ‘ Rapport.s presentes au Congres International de Physique,’ vol. 3, p. 138, Paris, 
1900. 
