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FEBRUARY I0, 1923] 
ox or some such animal, and I shall never forget the 
courteous way in which an eminent paleontologist 
assured him that the specimen should really go to the 
Museum at Bloomsbury, since a fossil would show 
only the bones, and not solidified flesh. The public 
certainly gets all it pays for, and more ; but it could 
be much better served if it would pay enough to bring 
out the latent possibilities of the museum, which are 
doubtless greater than any of us can yet clearly 
imagine. T. D. A. CoCKERELL. 
University of Colorado. 

Spiranthes Autumnailis. 
In the summer holiday of 1921, Mr. Mayland and I 
were astonished to find in the woods round Carrbridge, 
Inverness-shire, very sporadically but at two stations 
about a mile apart, specimens of the small orchid, 
Spiranthes autumnalis. We took some, and for two 
or three days their characteristic scent and spiral 
spikes interested our table in the hotel. I regret now 
t we did not preserve specimens: but I am pretty 
sure we were not mistaking the identity of the plant, 
as it was repeatedly the subject of remark, and I have 
known it since I was a boy. 
I mention this non-recorded record because Sir 
Herbert Maxwell, who in September 1920 wrote to 
Nature (vol. 106, p. 79), telling of a similar experi- 
ence on Lower Spey-side ; but ina later letter (vol. 106 
p. 409), he expressed some uncertainty as to the 
identity of his plant as Es pel from Goodyera repens. 
Now when so acute an observer as Sir Herbert has 
‘arrived independently at the same conclusion as we 
did, I think the probability is strong that both 
diagnoses were correct, and that, though the specimens 
were not preserved as evidence, S. autumnalis has been 
found in an unexpected, non-calciferous locality. 
Mr. Mayland tells me he sought it again in the 
following summer without result. F. O. Bower. 
The University, Glasgow, January 17. 

The Scattering of X-Rays in Liquids. 
In various notes published last year I dealt with 
the scattering of light in transparent media, and 
showed that its study initiated by the late Lord 
Rayleigh in his theory of the colour of the sky has 
other fascinating applications in the explanation of 
the colour of the sea and other transparent waters, and 
of the colour of ice on glaciers. The thermodynamic 
theory of ‘‘ fluctuations ’’ developed by Smoluchowski 
and Einstein formed the starting-point in the dis- 
cussions, but I was careful to emphasise the important 
complications arising from the anisotrophy of the 
molecules in fluid media and showed how the neces- 
sary corrections in Einstein’s theory may be made. 
A considerable measure of success was attained in 
attempting to correlate the behaviour of substances 
in the liquid and gaseous states in this respect, and in 
predicting the effects due to alterations of temperature 
and pressure. The study of the changes in the in- 
tensity and states of polarisation of the scattered light 
in passing from the liquid to the solid crystalline state 
and their explanation forms another important line of 
inquiry in which some progress has also been made. 
The purpose of the present note is to point out the 
relation between the optical effects referred to above 
and the very interesting recent work of Keesom and 
Smedt, who have obtained Laue photographs of 
various liquids traversed by a homogeneous pencil of 
X-rays (Proc. Roy. Soc. Amsterdam, 1922, page I19), 
and the similar work by Hewlett (Physical Review, 
December 1922, page 702), who used the ionisation 
method. Keesom and Smedt found that many of the 
NO. 2780, VOL. 111] 
NATURE 

185 

liquids studied gave a well-marked diffraction ring at 
a considerable angle with®the direct pencil. With 
liquid oxygen and argon, the first ring was formed at 
an angle of 27°. A weak second ring was also observed 
at 46° with oxygen, and at 49° with argon. With 
water, on the other hand, the second ring was very 
broad and diffuse and practically abutted on the first. 
Keesom and Smedt have attempted to explain their 
results by various special assumptions regarding the 
relative positions of the neighbouring molecules, while 
Hewlett suggests that liquids possess something of a 
crystal structure. To the present writer it appears 
that the experimental results may be explained with- 
out any such special assumptions. As in the optical 
case, the liquid molecules may be regarded as the 
diffracting centres which are arbitrarily orientated 
and distributed uniformly in space subject only to 
such variations as give rise to density fluctuations in 
accordance with the Einstein-Smoluchowski formula, 
Gpr= BP + Por 
where p, is the mean density (Ap)? the mean square 
of its fluctuations, R the gas constant, T the absolute 
temperature, 8 the compressibility of the liquid, and 
V the elementary volume under consideration. When 
traversed by a homogeneous pencil of X-rays the wave 
length of which is smaller than the average molecular 
distance, such a structure must give rise to diffraction 
rings which are more or less well defined according as 
the fluctuations of density are small or large. If in 
the expression for the density fluctuation, we take V 
to be a small cube with a molecule at each of its 
corners, the average fluctuation in its size and the 
resulting weakening of the diffraction pattern can be 
calculated somewhat on the same lines as in Debye’s 
theory of thermal effect in X-ray reflection by crystals. 
In Keesom and Smedt’s experiments, the low tempera- 
ture in the case of liquid oxygen and argon, and the 
consequently diminished fluctuations of density must 
have helped in improving the definition of the dif- 
fraction ring of the second order. C. V. RAMAN. 

‘« Artificial ’’ Vertical Beam. 
THE vertical beam through a low sun is generally* 
referred to the reflection of sunlight from the basal 
surfaces of thin plates of ice which are falling through 
the atmosphere with their crystal axes vertical and 
horizontal. It has been the writer’s good fortune to 
examine such reflections from individual “ plates ” 
that were slowly falling within a metre or so of the 
observer. Most of the plates were asymmetric portions 
of flat crystal growths, and they spun rapidly as they 
fell, with a motion resembling that of a falling maple- 
key. In this case, the vertical beam was observed to 
spread out slightly as it receded from the sun, and the 
angle subtended by the edges of the beam was obvi- 
ously the complement of the vertical angle of the 
“cone ’’ swept out by the rapidly rotating, but slowly 
falling flake. 
An interesting “ artificial ’’ example of (probably) 
this phenomenon, was noted by many observers at 
the burning of two buildings at the Sydenham Military 
Hospital at Kingston, Ontario, on the night of 
January 3, 1923. The structures burned fiercely in 
the brisk north-east wind and lit up the snow-covered 
country for miles around. The unusual brightness 
may be judged from the credible report that people 
more than a mile from the fire easily read newsprint by 
its light. A very light snow-fall was barely noticeable 
from time to time during the evening. Out of the 
glow of the fire-lit smoke clouds there appeared to 
rise a vertical parallel beam of light, that with varying 
distinctness was visible for the three or four hours 
F2 
