438 
NATURE 
[Marcu 10, 1904 
clearly I placed the screen nearly in contact with the eye. 
On touching the back of the screen with the finger, just 
under the luminous patch, there was seen to be a perceptible 
alteration in intensity of the light. 
On pressing the screen with the finger the light seemed 
to become less intense, and on removing the pressure the 
intensity was restored. A piece of metal, whether cold or 
hot, produced the same effect as the finger, and therefore 
vital action is not necessary for the phenomenon. 
At first sight it seemed as though the effect was caused 
by the muscular effort of the observer, for pressing the back 
of the head against a wall whilst the screen was in contact 
with the eye apparently made some difference in the bright- 
ness of the light, as also did clenching the hands, but in 
some cases the light was brighter and in others fainter, so 
that not much reliance can be placed upon the observation. 
Another person’s hand was as efficacious as that of the 
observer. 
I tried the experiment on two other persons without telling 
them what was to be observed, and in both cases they said 
““ the light is fading.’ 
The- experiment is very easily repeated, and it might be 
interesting to know whether it can be seen more readily 
than the n-ray manifestation. The screen must not be very 
bright; a zinc sulphide screen does not answer at all. 
W. A. Doucras Rupce. 
Woodbridge School, Suffolk. 
Earth Structure. 
MILNE, in reviewing Mr. T. Mellard Reade’s 
“The Evolution of Earth Structure, with a Theory 
” emphasises the demand at the 
“* pulsatory 
PROF. 
book, 
of Geomorphic Changes, 
present time for some theory which shall explain 
movements by which large tracts have been alternately 
raised and lowered.’’ Mr. Reade has attempted to supply 
the want, but, as Prof. Milne points out, his explanation 
is in some respects not very fundamental. 
Just before any solidification had occurred, the hot viscous 
gases which originally composed our earth, under the com- 
bined influence of gravity and diffusion, arranged themselves 
in such a way, each according to its density, that the 
heaviest swarmed towards the centre, where the pressure 
was also highest, and diminished in concentration towards 
the outside, where the pressure was at the same time lowest. 
In this way an infinite number of layers would have been 
formed, in which the change of composition varied 
gradually but continuously from the centre to the outside, 
and the total composition at depths far apart was widely 
different. When such a mass goes on cooling, where will 
solidification take place? 
The temperature of the earth’s centre is probably much 
higher than the critical temperatures of substances with 
which we are acquainted, and such substances would there- 
fore be gaseous there. Possible exceptions are the platinum 
metals, a few other elements, and endothermic compounds. 
The latter are quite stable and almost certainly easily 
formed at these temperatures and pressures, and they can 
also most probably remain solid at enormously high 
temperatures. If so, it is obvious that solidification in the 
mass of the earth’s gases would have very soon occurred, 
not merely on the outside, where the temperature gradient 
was always very steep, but at some one or more, ‘possibly 
deeply situated places where the layers happened to be of a 
composition more suitable in the circumstances, for the 
making of infusible endothermic substances—to us probably 
unknown—than those nearer the outside. There would 
then be layers of fluid sandwiched in between layers 
of solid. If we suppose the temperature coefficient of ex- 
pansion in these localities to be similar to those met with 
on the earth’s surface, any particular solid layer there 
would, as the whole earth cools, contract more quickly 
than the layers underneath it, until the solid would at 
length give way, and an escape of magma through the 
rupture “would relieve the tension. All the layers above, in- 
cluding the outer crust, would respond to this explosion; 
but in time the customary steady rate of cooling and con- 
traction would be resumed, which ultimately leading up 
to another “ blow off,’ would culminate in the continued 
repetition of the whole process. 
NO. 1793, VOL. 69 | 
Endothermic compounds can store enormous quantities of 
internal energy, which in suitable circumstances offering 
conditions of less stability can be discharged. ‘The simple 
rupture would therefore be complicated by the production of 
chemical changes, by expansion and contraction locally, and 
possibly even by regelation. If in the earth’s interior 
the coefficient of expansion increases with the temperature 
or with the pressure, there would be a tendency for the 
centre to shrink away from the layers above, and vesicles 
would result, as pointed out long ago by Fisher. As these 
vesicles would get larger and larger, a solid layer any- 
where here would be subjected to a strain as a result of 
the differential motion above and below it, and a collapse 
—obviously tending to become recurrent—would occur, 
which would ultimately affect the outer crust periodically 
or spasmodically. 
It is tolerably certain that under oceans the outer crust 
is much thicker than it is under the continents ; the tempera- 
ture gradients teach us this, and plumb-line measurements 
are also probably, most simply so explained. When a 
movement occurs below, we should consequently expect that 
the crust would ‘‘ give’? more under the continents than 
under the oceans. This would in the long run be an agency 
tending to counteract the effects of denudation, &c., so 
that continents should rise relatively to the oceans; and 
though no doubt local conditions could easily modify the 
easy applicability of this generalisation to any particular 
case, this seems an eminently useful conclusion. 
It is not at once obvious that there is anything, so far, at 
variance with any of the well-known facts discovered by 
the labours of Hopkins, Kelvin, Delauney, Darwin, Fisher 
and others; on the contrary, the joint results of their work 
seem to require a combination of solid and fluid which here 
appears to find adequate satisfaction. When it is so 
generally assumed that the first portion of the earth to 
solidify was the outermost part, it is, perhaps, not un- 
necessary to point out that that is, as a matter of fact, not 
quite true. In the atmosphere and hydrosphere we have the 
lightest—and fortuitously the most volatile—of those gases 
which originally cooled to make our planet. Quite irre- 
spective of what may happen below us, we know for certain 
that the outside of the earth must cool some 200 degrees 
before our descendants or their helium-breathing and 
demon-like representatives will find solid air among the 
constituents of the rocks under our feet. 
Kristiania, February 5 Cuartes J. J. Fox. 
Asymmetric Synthesis. 
Wirnout wishing to detract from the ingenuity displayed 
by Dr. W. Marckwald in his ‘‘ asymmetric synthesis ’’ of 
valeric acid, noticed in your issue of February 25, we desire 
to point out that it is not a true asymmetric synthesis in the 
ordinary sense. 
The ion of the acid or acid salt of ethylmethylmalonic 
acid may exist in solution in two enantiomorphously related 
forms 
coomM COOM 
| | 
CEE C=CHs ce 
| 
COO’ Coo’ 
On the addition of brucine the least soluble salt will 
crystallise out. This is no more than the resolution of an 
externally compensated ion by Pasteur’s well-known method. 
Both components of the salt will be active. The subsequent 
decomposition will, if no racemisation occurs, of necessity 
give rise to an active acid. Now this is a very different 
thing from the problem attacked by Fischer and Slimmer, 
Cohen and Whiteley, and Kipping. In these cases the 
original substance which is to be rendered active is not 
capable of existing in enantiomorphously related forms until 
it is submitted to chemical change in combination with the 
active substance. 
It is for this reason that we consider that Dr. Marckwald 
cannot claim to have accomplished a true asymmetric 
synthesis. 
J. B. Couen. 
T. S. Patrerson. 
The Yorkshire College, Leeds, February 26. 
