518 
MR. 0. W. RICHARDSON ON THE ELECTRICAI, CONDUCTIVITY 
Substituting the values of C and C' for d = 1571, O' = 1378 respectively, vre get the 
averao-e value of h from 1378° to 1571° absolute as 4-93 X lOh If rve assume that all 
o 
the work done by the corpuscles in passing through the surface is electrical, we 
can calculate from this the discontinuity in the potential. Since R is equal to 
( X 10■■l^ we have (h = 4*93 X X 10"^“ = eScf), where e is the charge 
1 204 / 1 .^04 
on an ion and B(f) is the discontinuity in the potential at the surface of the metal. 
From this we obtain 
S(f) = D365 X 10“^ electrostatic unit = 4‘1 volts. 
The further discussion of these results will he postponed until the experiments on 
sodium and carbon have been considered. (See additional Note at end of this paper.) 
II. Experiments ivith Carbon. 
§ 1. DescrijJtion of Apparatus. 
In order to detect and examine the negative leak from carbon, the hot wire 
previously employed was replaced by a filament from an ordinary 
incandescent lamp. The thick filaments from small 8 or 12-volt 
lamps were found to be most suitable. In the form of apparatus 
which was used to investigate the relatioin between the negative 
leak and the resistance of the carbon (see fig. 6) the filament was 
allowed to remain inside the lamp. The lamps were opened up by 
snipping off the glass point at the top with a pair of pliers. The 
wide tube A was then fixed on by drawing it out at the end which 
was to be joined and blowing tlie junction out until it was wide 
enouph to allow the aluminium electrode E to be introduced. This 
O 
jDiocess required some care, as the lamps are liable to crack when hot. 
It was found that air leaks due to small cracks in the part of the 
lamp which is covered with plaster of Paris could be effectually 
stojDped by embedding the whole lamp in melted j^araffin wax. The 
tube L, into which the electrode was fixed with sealing-wax, Avas 
joined to a bulb C, Avhich AA'as someAAdiat AAuder than A, into AAdiich it 
AAns inserted, the joints being made air-tight by means of sealing- 
unx. The side tube D led t(A the pump and McLeod gauge. The 
filament F could be charged either positively or negatively, and tlie 
leak from it to the electrode E Avas measured in exactly the same 
Avay as lias already been described in the case of platinum. 
T1 lis form of apjiaratus Avas found to be quite satisfactoiy for 
iiiAmstinatino- the connection lietAveen the current from the carbon on 
tlie one hand and the electromotive force, the I'esistance of the filament, and the 
