OcTOBER 30, 1913] 
NATURE 
267 
LETTERS TO THE EDITOR. 
[The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications.] 
The Reflection of 7 Rays from Crystals. 
In some recent investigations Prof. Rutherford and 
Mr. H. Richardson have analysed the y radiations 
emitted by a number of radio-active products. They 
have shown, for example, that radium B emits three 
distinct types of y radiation, which are absorbed ex- 
ponentially by aluminium with absorption coefficients 
#@=230, 40, and o-51 (cm.)~! respectively. On the 
other hand, radium C appears to emit essentially only 
one type of y radiation, the absorption coefficient of 
which is “=o0-115 in aluminium. 
Recently we have undertaken an examination of these 
types of radiation by the methods developed for X-rays 
by W. H. and W. L. Bragg, and by Moseley and 
Darwin, which consist in determining, either by the 
photographic or electric method, the intensity of the 
X-rays reflected from a crystal at different angles of 
incidence. In our experiments the source of y radia- 
tion was a thin a-ray tube containing about roo milli- 
curies of emanation, the y rays arising from the pro- 
ducts of the emanation, radium B and radium C. A 
diverging cone of rays fell on a crystal of rock-salt, 
and the distribution of the reflected radiation was 
examined by the photographic method. The source 
and photographic plate were each about 10 cm. from 
the centre of the crystal. Suitable precautions were 
taken to reduce to a minimum the effect on the photo- 
graphic plate of the primary and secondary 8 rays and 
penetrating y rays. The source was first arranged 
so that the radiation made an average angle of about 
9° with the face of the crystal. 
It was calculated from the known data of the 
crystal that the radiation »=40 from the radium B, if 
homogeneous, should be strongly reflected at about 
this angle. A group of fine lines comprised between 
the angles 8° and 10° have been observed on the 
photographic plate in a number of experiments. 
Similar results have been observed with a crystal 
of potassium ferrocyanide, kindly loaned to us by Mr. 
Moseley. On examining the reflection for an angle 
cf 2° another series of fine lines was obtained on the 
plate, probably resulting from the reflection of the 
more penetrating radiations from radium B and 
radium C. 
The experiments indicate that the y radiation for 
which “=40 is complex, and consists of several groups 
of rays of well-defined wave-length. Experiments are 
in progress to examine carefully the character of this 
reflected radiation, both by the photographic and elec- 
tric method. It is hoped that in this way definite 
evidence will be obtained on the constitution and wave- 
length of each of the types of y radiation which are 
emitted from radium B and radium C. 
E. RurHerrorp. 
E. N. pa C. Anprape. 
The University, Manchester. 
The Piltdown Skull and Brain Gast. 
Now that my friend Prof. Keith has explained 
(Nature, October 16, pp. 197-99) so lucidly his reasons 
for making a big brain-case of the Piltdown frag- 
ments it is possible to define precisely the point at 
issue between us. 
I should say at the outset that any anatomist, 
NO. 2296, VOL. 92] 
working with the plaster casts but without reference 
to the actual fragments from which they were 
moulded, might solve the extraordinarily difficult 
problem of reconstruction of the cranium in the way 
Prof. Keith has explained so plausibly. But the bones 
themselves present features which make such a solu- 
tion altogether inadmissible. Anyone who examines 
the left parietal and temporal bones cannot fail to 
; recognise that there is no room for any doubt as to 
the relative positions of these bones the one to the 
other, which is not that claimed for them by Prof. 
Keith. 
The right parietal fragment and the occipital can 
be put into their proper positions and the symmetry of 
the two branches of the lambdoid suture be restored 
without producing ‘“‘any marked asymmetry of 
another kind,’ such as troubled Prof. Keith, and 
without the necessity of making any such liberal addi- 
tions to the capacity of the cranium as he demands 
(see his Fig. 2). 
The “marked asymmetry of another kind” that he 
could overcome only by the adoption of the most 
drastic measures was created wholly by his refusal 
to admit the possibility that the middle line in the 
parietal region, as‘determined by Dr. Smith Wood- 
ward, was a close approximation to the truth. 
The determination of the précise location of the 
middle line in the frontal and parietal regions is one 
of quite exceptional difficulty, but a number of facts 
and considerations make it certain that it is not 
where Prof. Keith would place it. 
The crux of our difference, then, is the criteria 
which Prof. Keith uses for determining the middle 
line in the posterior parietal region. He writes (op. 
cit., p. 198 et seq.) :—‘‘In the skulls of all the higher 
primates, the longitudinal sinus, near the hinder end 
of the adjacent margins of the right and left parietal 
bones, is marked by a narrow deep groove with dis- 
tinct edges; on the margin of the upper angle of the 
Piltdown fragment the edge or margin of this groove 
can be clearly recognised.” 
It must be remembered that the area in question 
(the “upper angle” of the quotation) is immediately 
| above the middle part of the lambdoid suture, which 
is preserved upon the larger parietal fragment. Prof. 
Keith does not seem to have realised this fact, for 
he represents the lambdoid suture (in his Fig. 2) as 
a large arch (A, B, A, B) crossing the middle line a 
short distance below the larger bone fragment. If a 
series of human and simian cranial casts be examined 
it will be found that, contrary to Prof. Keith’s state- 
ment, in a considerable proportion of them there is 
no trace whatever (in the place just above the lambda 
corresponding to that preserved in the Piltdown 
| specimen) of “the narrow deep groove with distinct 
edges"’ on which Prof. Keith relies as his guide for 
the determination of the middle line. This is especially 
the case in the casts of the more primitive human and 
the simian crania, as Profs. Boule and Anthony have 
pointed out in their discussion of the Chapelle-aux- 
Saints and La Quina brain-casts. 
On these grounds Prof. Keith ‘‘moved the left 
parietal bone outwards or rather tilted [it] upwards 
and outwards until it assumes a more vertical posi- 
tion’? (p. 199). But in order to do this he had to 
get rid of one of ‘‘the peculiar features of the original 
brain-cast—the sharp bending inwards or kinking of 
the temporai lobe of the brain” (p. 199). If Prof. 
Keith had not opened out the angle between the left 
temporal and parietal bones the aperture of the ear 
would have been made to look towards the neck, 
when he ‘“‘tilted the left parietal upwards and out- 
wards”’! But the precise relationship of the left 
temporal and parietal bones is not a matter of argu- 
