OcTOBER 16, 1913] 
tinct edges; on the margin of the upper angle of the 
Piltdown fragment the edge or margin of this groove 
ean be clearly recognised. 
In Dr. Smith Woodward’s reconstruction, therefore, 
it is not only necessary to move the fragments of the 
right side outwards; the left parietal bone has also to 
be moved outwards, or rather tilted upwards and out- 
wards until it assumes a more vertical position, with the 
marking of the sinus in the middle line. When that 
is done, and the other parts correctly adjusted, the 
_ brain cast assumes the form and size represented in 
_ Fig. 2. I made many experiments to test other pos- 
sible suppositions, but only when the fragments were 
placed as in Fig. 2 could I secure symmetry, and at 
the same time obtain all the anatomical markings in 
their normal situations. The brain cast obtained from 
this reconstruction displaces just over 1500 cubic 
centimetres of water. Dr. Smith Woodward esti- 
mated his brain cast provisionally at 1070 c.c.; the 
replicas of the brain cast which were distributed 
displace 1200 c.c. of water; even if the reconstruc- 
tion carried out by Dr. Smith Woodward is accepted, 
and the right half is made approximately symmetrical 
with the left, the brain of Piltdown man will be about 
200 ¢.c. above his original estimate. 
In my reconstruction two other peculiar features of 
the original brain cast have disappeared. One is the 
sharp bending inwards or kinking of the temporal 
lobe of the brain; the other is the position of the 
foramen magnum—the opening in the base of the 
skull for the exit of the spinal cord. In the original 
reconstruction the lower margin of the occipital bone 
was brought forwards so far in the base of the skull 
that when a palate was articulated there was no 
room left for the soft palate and pharynx. The cor- 
responding basal parts of the brain cast are, of course, 
also abbreviated. 
I do not attach any high importance to actual brain 
mass; it is merely a rough indication of mental 
power when applied to human brains. So far as 
concerns the description of the actual markings of 
the Piltdown brain cast given by my friend Prof. 
Elliot Smith, I am in complete agreement, but so 
far as concerns general mass and conformation, it is 
clear, from his letter in Nature, October 2, p. 131, 
that I am at complete variance. How far I am right 
—to what extent I have made an error—remains to 
be seen; but the publication of these drawings and 
observations will show that I have made every 
endeavour to arrive as’near the truth as is possible 
for me. A. Kern. 
Royal College of Surgeons, Lincoln’s Inn 
Fields, W.C., October 4. 
The Theory of Radiation. 
In his letter published in Nature of October 9, Prof. 
Maclaren has referred to my use of the concept of 
a natural unit of angular momentum, and perhaps 
a few explanatory remarks may be useful, as the work 
has not been published in a journal devoted to physics. 
The concept first appeared in my paper on the con- 
stitution of the solar corona, published in the Monthly 
Notices of the Royal Astronomical Society in June of 
last year. It was found that the energy frequency 
ratios of the atomic systems, which were held to be 
the origin of the main lines in the coronal spectrum, 
were always simple multiples of the quantity h/27, 
where h is Planck’s constant. As these ratios were 
nothing more or less than the angular momenta 
of the atoms, the conclusion was forced upon me that 
Planck’s h could only be an angular momentum. 
As was stated at the time, such an interpretation 
removes much of the difficulty otherwise pertaining 
to the quanta theory, when expressed in the usual 
NO. 2294, Vol. 92| 
' NATURE 
199 
Way in terms of energy. It does not, of course, ex- 
plain that theory, but merely renders it more intelli- 
gible as a possibility, for it is not difficult to obtain 
fair mechanical models of atoms the angular momen- 
tum of which can only have a discrete set of values. 
Prof. Maclaren, in his letter has, in fact, indicated 
a very beautiful one by the help of the magneton, 
which has a definite unit of angular momentum. It 
is evidently possible to construct a system containing 
multiples of that unit. ; 
The more recent work of Dr. Bohr (Phil. Mag., 
July and September of this year) applies the same con- 
cept to series spectra, but is different in that it postu- 
iates the angular momentum of an electron in the 
normal state of the atom as exactly h/27. For 
example, the whole angular momentum of a neutral 
atom with five electrons is, on Bohr’s theory, 5h/27. 
But I had found it necessary in the paper cited above 
that the value should be 25h/27. There is in this 
respect a discrepancy between the two theories, which 
is probably not serious, as Dr. Bohr has only calcu- 
lated the series linesin hydrogen and in helium with a 
single electron, and therefore charged. (The number 
of electrons and its square are then identical.) The 
real test of his theory will lie in its capacity to account 
for the usual spectrum of helium—a test which does 
not appear difficult. For’ Dr. Bohr has concluded 
that helium will not take a negative charge. The 
ordinary spectrum must therefore come from the un- 
charged atom in its passage between stationary states, 
which are of a limited number, as there are only two 
electrons. It does not appear that the helium spec- 
trum can be obtained in this way, but perhaps further 
investigation will modify this conclusion. Until this 
is done, the point raised by Prof. Fowler in a recent 
discussion in NATURE, as to the apparent need for 
xeeping the Balmer and Pickering spectra of 
‘““hydrogen”’ as two distinct series, has not been 
answered. 
But as Prof. Maclaren states, whatever be the fate 
of this theory, the natural unit of angular momentum 
seems necessary. It is inevitably suggested by any 
atomic theory which now attempts to rest on a founda- 
tion of electrons and a positive nucleus; for its use 
is not restricted to the applications already mentioned. 
It is apparently the only ready means of explaining 
a type of spectral series which the writer has found 
recently to be of importance—a series in which the 
cube roots of the wave-lengths have constant differ- 
ences. J. W. NicHoLson. 
King’s College, London. 
Science and the Lay Press. 
Many “lay” journalists will have welcomed the 
comments in Nature of October g (p. 172) on the 
“sensational paragraphs to the effect that Sir 
Frederick Treves had announced at the Radium In- 
stitute ‘a complete revolution in the future of 
radium.’’’ For the undue enthusiasm shown, the 
Radium Institute is partly to blame. Sir Fredericl 
claimed credit on behalf of it for the discovery that 
emanation was as valuable as radium in the treat- 
ment of cancer, and when Mr. Pinch was describing 
the good results obtained with emanation water in 
the treatment of arthritis deformans he interpolated 
the remark that this was something new in medicine. 
Undoubtedly, too, the impression was created in the 
minds of many of those present that by utilising 
emanation a gram of radium could be made to do 
the work of several grams. While in the matter of 
comment several newspapers fell into gross errors, 
they did little more than translate into popular 
language the sense of what was said. 
Unfortunately in compressing what he had to say 
