IMPARTED TO A VACUUM BY HOT CONDUCTORS. 
541 
It will be noticed that the two curves belonging to any one set of observations 
become parallel above about 180° The constant distance apart of the curves, which 
is approximately the same for the two sets of observations when measured along the 
vertical ordinate, has an average value of about 1 '6. This shows that the ratio of the 
currents in opposite directions remains constant and independent of the temperature 
(above 180°) and is equal to about 40 to 1. The point of inflexion at about 280° on 
the up curves probably indicates an accidental change in the sodium surface, since it 
was not repeated on cooling. 
C.—Conclusion. 
§ 1. The Determination of the Number of Ions in a Cubic Centimetre of Metal. 
The preceding results show that the number of negative ions produced by one 
square centimetre of surface of platinum, carbon, and sodium at temperature 6 can be 
represented with fair accuracy by the formula N = = k^n6^e~^'\ where A 
and b are assumed to be deflnite constants for each metal. As an empirical result we 
And A and b have the values given in the following table :— 
Conductor. 
A. 
b. 
Platinum. 
1026 
4-93 X 101 
Carbon . 
103-1 
o 
X 
00 
9-7 X101 
11-9 xlOi 
Sodium. 
1031 
3-16 X101 
