536 - Lord Kelvin on Electric 
or 320,000 C.G.S. electrostatic. Taking with this J. J. 
Thomson’s most recent estimate* e=3'4.10— C.G.S. 
electrostatic, for the quantity of resinous electricity in an 
electrion, we find 109. 10-° dyne as the force which a single 
electrion would experience in the electrostatic field between 
the electrodes in these circumstances. 
§ 7. Consider now a single mono-electrionic atom having 
a single electrion within it, in equilibrium in the centre of 
the field. Let be the radius of the atom, and « the distance 
from its centre, at which the electrion rests. The electro- 
static force at distance « from the centre is : . = and 
therefore if the force of the external field is just sufficient to 
9 Qey Sh 
make “225 'we have ° 7-197" 2390000.) "7nn 
no 9 i 
rel bos +s: 
§ 8. Consider next an equal and similar atom in the extreme 
front of the kathode. Its electrion will certainly be drawn 
to a considerably greater distance from its centre than 4 7; 
because it is backed by atoms behind it with their electrions 
pulled forward : it is probable, however, it could not be quite 
extracted from the atom without a greater electrostatic force 
than that considered in § 6. But it seems to me certain, from 
some imperfect mathematical reckonings which I have made, 
that from two to four or five times that force would suffice to do 
so. We shall guess it as 1,280,000, being four times that force : 
though the actual amount required is calculable and would 
certainly be different for ditferent possible crystalline con- 
figurations of the molecules in the kathode. ‘Thus, merely 
as an illustration of the orders of the magnitudes concerned, 
we shall assume that, with 2°2 . 10-8 for the diameter of the 
atom and 3°4.10-1° C.G.S. for the quantity of vitreous elec- 
tricity in the atom and of resinous in the electrion, an 
electrostatic force of 1,280,000 C.G.S. in the ether in front 
of the kathode would break down the insulation by drawing 
off electrions from the outlying atoms of the kathode. 
§ 9. Leaving atomic considerations for a moment, remark 
that, per unit area, the outward attraction experienced by a 
metallic surface under the influence of electrostatic force R 
in the air, or the ether, outside is R?/87. This with 
R=1,280,000 gives 6°519X10" dynes or approximately 
66°4 tons weight per square centimetre. The breaking 
weight of the strongest steel wire scarcely amounts to 20 tons 
* ‘Electricity and Matter,’ p. 78 (1904). 
+ See Baltimore Lectures, Lect. xvii. § 80. 
