Insulation in “ Vacuum.’ 537 
per square centimetre. Hence the thick straight wire of § 6 
would be broken or would have its electrified end shattered 
and pulled away in fragments by the electrostatic force sug- 
gested at the end of §8. It would, however, bear without 
breaking, and possibly without any disintegration of its 
electrified end, the 320,000 C.G.S. of § 6, which would only 
strain the wire with a force of 16°6 tons weight per square 
centimetre. 
§ 10. Moderate permissible changes in our guess-work 
assumptions regarding sizes and electric quality of atoms 
(mono-electrionic or poly-electrionic) might no doubt readily 
be devised to make the discharge of electrions take place 
with increasing electrostatic force, before disintegration of 
either kathode or anode is produced. We have as yet no sure 
experimental evidence as to what would take place in the 
perfect vacuum (only ether, no ponderable atoms, in the space 
between the electrodes) which is our present subject. What 
has been observed in respect to the highest of modern vacuums 
(from one one-millionth to one two-hundred-millionth of an 
atmosphere by the Macleod gauge), shows that a much greater 
difference of potential than 100,000 volts (which is so far as 
I know the highest hitherto measured electrostatically) may 
be maintained between two metallic electrodes without pro- 
ducing a manifest discharge through the “ vacuum,” even 
when the electrodes are brought within less than 1 mm. of 
contact. And whena discharge does take place it is I believe 
not generally direct between the nearest points of the ends 
of the electrodes, but in wildly erratic lateral courses, attri- 
butable to residual gaseous molecules, according to J. J. 
Thomson’s experimental and theoretical investigations on the 
passage of electricity through gases. 
§ 11. Inthe experiments by which Varley discovered the 
kathode torrent of resinously electrified particles, the differ- 
ences of potential used were those of a Daniell’s battery of 
from 307 to 380 Daniell’s elements. The fact that such small 
electrostatic forces produced luminous discharge, proves that 
his vacuum was very far from being what is now called a 
high vacuum: and proves that the molecules of the residual 
air were largely concerned in all his results. It is exceedingly 
interesting to learn from J. J. Thomson’s experiments of 
1897, described in §50 of his ‘Conduction of Electricity 
through Gases’ that, great though the influence of the 
residual gas (air or hydrogen or carbonic acid gas) was in 
‘respect to the results, the virtual mass of the resinously 
electrified particle in the kathode torrent is the same for the 
different gases ; and is about 1/770 of that of the hydrogen 
