642 

failure to detect any charging effect, as a result of the 
influx of corpuscles, in the case of a mass of insulated 
metal surrounded by a thin metal shield to protect it 
from the potential gradient. The second arises from 
the fact that, in so far as the replenishment of the 
earth’s charge requires the entry of 1500 corpuscles per 
sq. cm. per second, and, a corpuscle moving with a 
velocity approximating that of light produces about 
4o ions in each centimetre of its path, we should expect 
a rate of production of 60,000 ions per c.c. per second. 
Experiment reveals a rate of production of less than 
ro lons per c.c. per second, and these are attributable, 
for the most part, to known causes. 
As regards the former difficulty, experiments to 
detect the charging effect were made by the writer in 
1915, and more recently by von Schweidler, without 
finding any such effect. Unless we assume corpuscular 
ranges so great that there is negligible absorption in the 
test body, this result opposes any theory which invokes 
corpuscles shot into the earth from regions outside 
our atmosphere, or from the atmosphere itself as a 
result of direct spontaneous disintegration. The ex- 
periment is not so much in conflict with theory in the 
case where the corpuscles are emitted by the pene- 
trating radiation, however. If the penetrating radia- 
tion is sufficiently hard to pass through the test body 
without appreciable absorption, it can be shown that 
it will eject as many corpuscles from the lower side of 
the body as it injects on the upper side. 
Serious as the difficulty concerned with the ionising 
action of the corpuscles seems at first sight, there is a 
natural way of avoiding it, providing that we assume 
the corpuscles to have velocities so closely approximating 
the velocity of light that their tubes of force become 
crowded very greatly towards the equatorial plane. 
In these circumstances, if a corpuscle ? is to give even 
a small finite amount of energy to an electron in the 
process of ejecting it from an atom, it must give it in 
an infinitesimal time, and such a phenomenon would 
require the payment of an infinite tax in the form of 
energy radiated. A full consideration of the details of 
the action shows that the reaction on the electron, due 
* The word “corpuscle” is merely used to distinguish the high-speed 
electron, the ionising powers of which are under discussion, from the electron 
in the atom, 
NATURE 

[May 12, 1923 
to its radiation, is such that, for any ionisation potentiai 
of the atom, there is a velocity sufficiently near to that 
of light, such that a corpuscle having that velocity 
would be unable to produce any ionisation in the gas. 
The ionisation potential of oxygen, which is less than 
that of nitrogen, is 15:5 volts, €nd on the classical 
theory of electrodynamics a corpuscle would fail to 
ionise oxygen or nitrogen for all velocities in excess of 
200 metres per second below the velocity of light. It 
may be of interest to remark that, in order that an 
electron should strike down into our atmosphere in the 
vicinity of the equator and reach the earth’s surface, 
without being bent back by the earth’s magnetic field, 
it would have to possess a velocity nearer to that of 
light than the above value, so that the very fact that 
it could reach the earth would be sufficient to ensure 
that it would not ionise on the way. Moreover, as 
another illustration of the same principle, it may be 
remarked that the above value for the velocity lies 
between the two limits, 400 metres per second less than 
that of light, and 4 metres per second less than that of 
light, assigned by Birkeland as the limits between 
which the velocities of negative electrons from the sun 
must lie in order that they shall be capable of accounting 
for the aurora. Of course, failure to ionise would pre- 
vent corpuscles from functioning as regards the aurora, 
and the figures in question are only cited for their~ 
general interest. There are other reasons for believing 
that the aurora is not caused by negative electrons. 
Once we assume these high energies for the corpuscles, 
they carry with them the possibility of very great 
penetration, as may be shown from a consideration of 
the circumstances which determine absorption in the 
atmosphere. This penetrating power is enhanced by 
the diminution of the power of the corpuscles to com- 
municate energy to the electrons by which they pass. 
Thus, while, as regards the mere explanation of the 
earth’s charge, we may avoid the assumption of long 
ranges, as in the theory which invokes the penetrating 
radiation to eject the corpuscles from the air, we find it 
necessary to postulate, for the corpuscles, velocities — 
closely approximating the velocity of light, in order to 
explain the absence of ionisation, and this of itself im- 
plies long range as a consequence. 
(To be continued.) 
The Royal Academy, 1923. 
if Bae private view of this year’s Exhibition of 
the Royal Academy took place on Friday, 
May 4. The juxtaposition of the Royal Society and 
the Royal Academy suggests something deeper than 
the accident of both being dependent upon the patron- 
age of the wealthy and the hospitality of the State. 
On either side of the wall that separates the academies 
of art and science the work is alike also in this—the 
impulse of the worker is to represent and thereby to 
preserve the visions that he has seen, that others 
might have seen if they had been gifted with the 
insight that sees things hidden from the rest of the 
world by the blinding candour of Nature. One uses 
paint or clay, and the other the printing-press or the 
experimental table; and however dependent either 
may be on the smile of the wealthy or the favour of 
NO. 2793,-VOl iat) 

‘ 
the potentate for the means to “carry on,” the satis- — 
faction of achievement in the effort to express what 
they alone have seen with the mind’s eye redresses 
for either the adverse balance of many an account. 
A year’s Proceedings of the Royal Society show what 
the fellows wish to hand on to posterity as expressing 
their searching into Nature: so the yearly exhibition 
at Burlington House represents the messages to which 
the artists of to-day have dedicated their power of 
insight. 
Passing through the galleries for the first time one 
wonders what message the artist is trying to convey 
and whether he has succeeded. There can be little 
doubt that 200 (Still Life, by Meredith Frampton) 
aspired to give the impression of china ducks and 
flowers, and has succeeded; and the same may be 
