Marcu 18, 1915] 
NATURE 
65 


London. It is impossible to say whether the others | 
arrived in Brussels, and, if so, what has now become 
of them. Dr. Christy’s list is a very interesting one, 
and I will venture to give extracts from it. The 
specimens are distinguished by numbers. ‘‘No. 507, 
do juv., not full grown; shot by myself, April 10, 
1913. Skin good, skeleton complete.” ‘*No. 531, 
dG, full grown. Shot by a Congo official, out shoot- 
ing with me, May 22, 1913. Horns 12 in., skin- 
covered. Skin good, skeleton complete.” ‘* No. 686, 
2, big. Shot by myself, October, 25, 1913. Skin 
good, skeleton complete.” ‘‘No. 717, ¢, old. Shot 
by Reid. Skin good; horns and hoofs attached to 
skin. Skeleton complete. Horns 4 or 5 in. long, and 
bare at tips.” ‘‘No.'532, ?¢. Skin only: from 
natives.” “No. 533, ?'2. Skin only; from natives.” 
“No. 695, juv., ?sex; half-grown, 1913. Skin dried 
by natives. Skeleton complete.” 
In this list it will be observed that nothing is said 
about ‘‘horn-sheaths.’’ It is perfectly certain that, as 
a sportsman and naturalist acquainted with the okapi, 
and the only ‘educated’? European who has himself 
shot the okapi, Dr. Christy would have directed 
attention in his notes to the presence of ‘horn- 
sheaths” if he had discovered such structures to exist. 
Only one of the seven specimens mentioned in Dr. 
Christy’s list has come through to London. I have 
no doubt that it is the specimen No. 531, shot on 
May 22, 1913, at Mawambi, by a Congo official out 
shooting with Dr. Christy. The horns (ossicones) 
are stated definitely to be skin-covered. This agrees 
with my inference from a comparison with the Boyd 
Alexander specimen and the state of growth of the 
ossicones. It makes the “ horny-sheaths”’ impossible. 
The measurement given by Dr. Christy for the horns 
(ossicones) is 13 in. This is their Vertical height 
from base to apex. As they are pyramidal in shape, 
the measurement along the side of the pyramid from 
apex to edge of the expanding base, is as given 
above by me, about 2 in. 
I think that Dr. Christy’s own notes settle the 

question against the horny sheaths which it was 
already really impossible to “ fit ” satisfactorily to the 
specimen with which they reached Mr. Gerrard. 
As to how this label—with ‘‘ Horns of the Okapi ”’ 
written on it—became attached to these little horn- 
sheaths it is possible to form various conjectures. 
Perhaps some busy, well-intentioned servant, being 
told to be sure to see that the little horns (ossicones) 
were not omitted from the parcel, mistakenly picked 
up the small horn-sheaths belonging to some antelope 
skin, left by chance with other skins and skulls in 
the disorder of packing or preparing a mass of speci- 
mens, and conscientiously but erroneously labelled 
them ‘‘Horns of Okapi,” and packed them with 
specimen No. 531, destined to produce astonishment 
and confusion on arriving two years later in London. 
Dr. Christy is to be congratulated on the fine series 
of specimens of okapi which he obtained and sent to 
Brussels en route for London. We must hope that 
they may escape destruction or seizure by the enemies 
of mankind, and eventually yield their contribution to 
our knowledge of the okapi, especially since among 
them are the first specimens seen alive and shot by a 
competent European observer. 
March 9. 

E. Ray LankestTer. 

The Spectra of Hydrogen and Helium. 
Mr. E. J. Evans has described recently some in- 
teresting experiments on the ‘ 4686" and Pickering 
series, which were obtained from vacuum tubes con- 
taining helium from which hydrogen was apparently 
completely eliminated. Stark has also observed the 
“4686” line in a vacuum tube showing no trace of the } 
NO. 2368, VOL. 95] 
res ek, 
hydrogen lines. The experimental evidence of a 
helium origin of the lines in question would. thus 
appear. to be strong, and Prof. Fowler, from analogy 
with the enhanced line series of the alkaline earths, 
has also concluded that the lines are due to helium. 
According to Dr. Bohr, who first suggested that the 
lines were due to helium, the series in question owe 
their origin to the binding of an electron by a helium 
atom from which two electrons have been removed. 
Dr. Bohr’s theory involves a modified value of Rvyd- 
berg’s constant for these lines, and Prof. J. W. Nichol- 
son, in a letter to Narure of February 11, has pointed 
out that it can be put to the test by an accurate 
measurement of the lines of the “4686” series, from 
which the value of the constant can be calculated. 
Although the spectroscopic evidence is in favour of 
helium as the origin of the lines, it may be pointed 
out that this evidence is not conclusive. Although 
4686 does not appear in hydrogen in the absence of 
helium, the same may be said of ultra-violet members 
of the Balmer series, which do not appear in vacuum 
tubes containing pure hydrogen, but which make 
their appearance when helium is present. The diffi- 
culty of preparing vacuum tubes free from hydrogen 
is well known, and the fact that the ordinary hydrogen 
lines are absent from the spectrum cannot be taken 
as conclusive evidence that hydrogen is not present. 
In view of this fact, the writer has conducted experi- 
ments to determine the relative mass of the atom 
from which the ‘‘ 4686” series originates, by measur- 
ing the limits of interference of the “4686” line and 
the lines of helium and hydrogen. The circumstances 
which control the breadth of spectrum lines have been 
discussed by Lord Rayleigh in the current number of 
the Philosophical Magazine. 
At low pressures the order of interference at which 
fringes are still visible is proportional to the square 
root of the atomic weight of the atom from which 
the radiation originates. It is hoped shortly to pub- 
lish a full account of the experiments, but the follow- 
ing may be stated as a preliminary result. A vacuum 
tube containing helium and hydrogen at a low pressure 
was excited by an induction coil with capacity and 
a _spark-gap in the circuit, the spectrum consisting 
of helium lines, 4686, and the hydrogen lines. With 
an interference apparatus giving a suitable difference 
of path, moderately sharp ring systems can be ob- 
tained for all the helium lines, whilst no trace of 
interference can be detected in the 4686 line or the 
hydrogen lines. 
Further observations are required to determine the 
exact limits of interference of the 4686 line and the 
hydrogen lines, but the results indicate that the mass 
of the atom from which 4680 originates is definitely 
smaller than that of the atoms concerned in the pro- 
duction of the ordinary helium spectrum. 
T. R. Merton. 
University of London, King’s College, March 15. 

Musical Sand in China. 
AMONG the immense mass’ of ancient Chinese 
records and manuscripts brought back from the buried 
cities and caves of ancient Khotan, in Central Asia, 
and now stored in the British Museum, is one called 
the Tun-Huang-Lu, a_ topographical description of 
part of Khotan itself. This little geography was 
written in the time of the Tang dynasty, in the 
seventh century, but probably contains matter from 
earlier authors, 
Among the specially interesting natural phenomena 
of the country described in the Tun-Huang-Lu is a 
large sandhill, which at certain times gave forth 
strange noises, so much so that a temple in its 
vicinity was entitled the ‘‘ Thunder Sound Temple.”’ 
