547 
IMPARTED TO A VACUUM BY HOT CONDUCTORS. 
placed between the ends of the filament of an incandescent lamp, tlirongh a galvano¬ 
meter to the positive end of the filament. A current was then oliserved which 
amounted in some cases to several milliamp^res, although there was no current when 
the electrode was joined to the negative terminal. Evidently the current was carried 
by corpuscles passing from the negative portions of the hot carbon to the relatively 
positive electrode; and, on this view, we should expect the current to vanish by 
comparison when the electrode was negative with respect to the filament. 
This observation was confirmed and extended Ijy Professor Fleming,* who showed, 
by using cylindrical electrodes which he placed round various parts of the filament, 
that the current only came from the negative end. He also found, in agreement 
with the results of the present paper, that a platinum filament likewise gave an 
eftect. This was in the same direction as, but greater in magnitude than, that given 
by caibon. Finally, the Edison efiect was found to increase rapidly with the 
temperature of the filament, which confirms its identification with the phenomena 
here investigated. 
§ 5. The Energy Emitted. 
It IS of interest to compare the energy lost liy a hot body owing to the emission of 
corpuscles with the energy given off in the form of electro-magnetic radiation. The 
recent measurements of E. KurlbaumI' show that the energy radiated in 1 second 
from 1 sq. centini. of the surface of an absolutely black body at 1° absolute is 
S = 2-12 X 10-4 -_, 
centnn. sec. deg.^ 
whilst we have seen that the total rate of loss of energy of a conductor owing to the 
emission of corpuscles at temperature 9 absolute is 
E, = n {1 + <fi/2Kd] 
^ irm 
Since the quantities and n in this formula liave now been determined for carlion 
and platmum, we can calculate E at any temperature for these substances. The first 
term in brackets represents the part of the energy due to the motion of translation of 
the emitted corpuscles, and is less than 5 per cent, of the second term at all 
temperatures at which experiments have been carried out. We may therefore leave 
it out to a first approximation and calculate only the second term, which is equal to 
the work done by the corpuscles in passing through the surface layer. Tliis is 
obviously equal to NT) 
- CoSff, 
* ‘Phil. Mag.’ [.5], vol. 42, ji. 52. 
t ‘ Wied. Ann.,’ vol. 65, p. 759. 
4 A 2 
