Conduction of Electricity through High Vacua. 157 
considerably smaller than in air, is produced by the traces of 
oxygen remaining. 
The observations in Table IV. show no regular increase of 
loss of weight with increasing cathode-fall. In several cases 
a limit seemed to be reached at a comparatively low potential, 
beyond which there is no increase in disintegration. The 
loss in weight of silver and nickel, which is approximately 
constant, agrees fairly with Faraday’s law, while iridium 
and rhodium disintegrate much less. 
Physikalisch-Technische Reichsanstalt, 
February 1904. 
XVI. Conduction of Electricity through High Vacua, under the 
influence of Radvoactive Substances. By Hon. R. J. StRvurv, 
Fellow of Trinity College, Cambridge*. 
T is a matter of no great difficulty to detect the negative 
charge carried by the @ rays of radium ; butall attempts 
to observe directly the positive charge carried by the @ rays 
have hitherto been unsuccessful. [have recently made some 
experiments on the subject, which have satisfied me that even 
in high vacua there is a loss of electricity from a charged 
body, in presence of the a rays, independent of traces of 
residual gas. This effect necessarily defeats any attempt to 
detect the charge of the @ rays. 
A rod of bismuth made active by a deposit of “ radio- 
tellurium” was used. This emitted « rays only, and thus 
any complication due to the negative charge of the @ rays was 
avoided. A further advantage was the absence of any 
gaseous emanation. The rod was attached to an electroscope, 
and the whole arrangement hung up by an insulating support, 
in a vessel which could be exhausted very much after the 
manner described in a former paper (Phil. Mag. Nov. 1903)+. 
By means of an iron wire, movable by an external magnet, 
the insulated system could be charged up when desired. 
The position of the leaf was read by a microscope, as usual. 
The apparatus was connected to a Topler pump, a manometer, 
and a Rontgen focus-tube, which latter served to show when 
a realiy good vacuum had been attained. 
The system was charged, and the rate of loss of the charge 
measured at varlous pressures, At pressures of from 300 mm, 
-* Communicated by the Author. 
+ Some experimenters have experienced difficulty in projecting that 
apparatus on the screen owing to radiometer effects. I have not found 
this, using a limelight, and a thick alum cell to absorb heat, 
