ct 
# 
410 Prof. J. Trowbridge and Mr. W. Rollins on 
in air gave curves with two maxima, similar to those obtained 
with platinum ; but under the same conditions as regards 
strength of discharge-current, time of exposure to the dis- 
charge and pressure of air in the discharge-tube, the emis- 
sibility due to aluminium appeared to be smaller in amount 
and to furnish maxima at lower temperatures than that due 
to platinum. 
Ai present it seems premature to discuss at any length the 
numerous theories which suggest themselves’ as to the 
mechanism by which these effects are produced. It seems 
probable, however, that the effect is connected with the de- 
position of a material substance on the surface of the testing 
wire, and it is likely that the phenomenon is connected with 
cathodic disintegration. The effect simulates in a qualitative 
manner the consequences of the theory of monomolecular 
decomposition suggested previously; but, perhaps owing to 
the complexity of the conditions, the author has not been 
able to establish the results quantitatively as yet. 
Before concluding, the author wishes to,,cerrect an erro- 
neous conclusion trom the experiments on the emissibility 
imparted by exposure to air described on pp. 90, 91 of the 
paper already referred to*. Apparently the reviving effect 
obtained in these experiments was not due to air at ‘all, but 
to some obscure gas or vapour which was let in along with it, 
Recent experiments seem to indicate that in some cases the 
apparatus gets full of a gas which has a very powerful re- 
viving effect, a phenomenon which is under investigation at 
present. It may be of interest to mention that a platinum 
wire which has been heated until it has lost its leaking 
power, and subsequently sealed up ina good vacuum, does not 
show any appreciable recovery when left for a period of three 
weeks. 
In conclusion the author wishes to thank Prof. Thomson 
for his kind encouragement and valuable suggestions during 
the course of this investigation, which was carried out in the 
Cavendish Laboratory. 
hy, rain and the Electron Theory. 
By Joun Trowsriper and WittiAM Row.iyst. 
HE mechanism of electric conduction through metals 
continues to be one of the greatest mysteries of elec- 
tricity ; and there is no plausible explanation of it unless we 
accept the theory of electrons. 
This theory, as is well known, supposes the existence of 
small bodies called electrons, which move between the mole- 
cules of the metals during the passage of an electric current. 
© Phal Mae.9ol voll yi. p81, 
7 Communicated by the Authors. 
