762 REPORT—1 885. 
Probably, however, one is now not on the right track, and it is better 
to refrain from further guess-work ; though I must just point out that if 
one reckons the distance at which fully charged atoms would be able ta 
cling together, on this hypothesis, if they are to give ordinary dielectric 
strength, though it is too great to be reasonable, it is not outrageously 
so. ‘The simplest plan is, perhaps, just to quote the arithmetic. 
To reckon the greatest atomic distance when the atoms of a molecule: 
are just being torn asunder electrically. Call it y. 
The actual stress which can be supported by ordinary air, according 
to experiment, is given by the equation 
= p = } gramme weight per unit are 
so a centimetre thickness can stand V = 110 electrostatic units, or 
33,000 volts. 
This would give a force of 110 dynes per electrostatic unit, 
or 110°% 15 10-2 65x’ 10 per atom: 
The attracting force of two atoms, at distance y, is ct 
y 
So when a molecule is on the verge of giving way, 
ete KO, 5. aan 
“ee Sh 
or y = 3°65 x 10~’ centimetres, when just giving way. 
This is for common air, and is much too big: a stronger dielectric 
will be satisfied with a smaller limiting atomic range, though still not 
with one small enough. 
It is difficult to suppose that molecules tend to get separated instead 
of atoms, and that accordingly ordinary mechanical, not chemical, tenacity 
is the force to be overcome in a dielectric ; for how can this apply to the: 
case of a liquid or a gas? 
in pure dry air: as the following table shows. Though indeed the fourth root of: 
the pressure would do better still. 
Minimum Potential| Pressure & 
| ve 
639 615 75 
577 499 73 
503 385 €9 
402 198 69 
301 68 74 
258 29 84 
198 10:9 90 
189 we 98 
