A Remarkable Meteor on November 24. 
I was much interested in seeing Dr. Rambaut’s 
letter describing a brilliant meteor seen at Oxtord 
on the evening of November 24. I was travelling 
along the London to Oxford road at the time, and 
when passing through Stokenchurch (seventeen miles 
from Oxford) was suddenly aware of a pale green 
light of sufficient intensity to be quite noticeable even 
when looking down at the road. On looking up I 
saw the meteor just as it disappeared. It presented 
the appearance of a luminous green ball of about 
one-quarter the sun’s diameter, though this can only 
be regarded as quite an approximate estimate. My 
first impression was that the phenomenon was an 
unusual type of meteor, but on account of the brilliant 
green colour | immediately afterwards came to the 
conclusion that it must have been a rocket, and there- 
fore did not unfortunately note the exact time or 
careful particulars as to the position. I should esti- 
mate that the meteor lay about N.N.E. when I saw 
it, but that the altitude was somewhat greater than 
the 17° given by Dr. Rambaut. The agreement in 
time and ‘place was, however, sufficiently close to leave 
no doubt that it must have been the same pheno- 
menon. The intensity of the illumination may be 
judged from the fact that the light was quite notice- 
able to one not looking up towards the sky at the 
time. J. S. Dives. 
Meteorological Office, South Farnborough Branch, 
December 1. 
I REGRET to have to have to point out a mistake 
in my letter printed in Nature for November 27 
(p. 372). The altitude of the meteor should have 
been given as 27°, not 17°, as there stated. 
As the error appears in my copy, I fear I must bear 
all blame for it. ArtHUR A. RAMBAUT. 
Radcliffe Observatory, Oxford, December 1 
THE BRITISH RADIUM STANDARD. 
AS account of the preparation and testing of 
an international radium standard was given 
in the issue of this journal for April 4, 1912 (vol. 
Ixxxix., p. 115). It will be remembered that a 
radium standard containing 21°99 milligrams of 
pure radium chloride was prepared by Mme. Curie 
for the International Committee. At a meeting in 
Paris the standard of Mme. Curie was compared 
with another independent standard prepared in 
Vienna by Professor Hénigschmidt, and the two 
were found to agree well within the limits of ac- 
curacy of measurements by the y ray method. The 
preparation of Mme. Curie was accepted by the 
Committee as the International Standard, and 
was deposited in the Bureau du Poids et Mesures 
at Sévres, near Paris. At the same time it was 
arranged that the Vienna preparation should be 
retained in Vienna as a secondary standard. 
Arrangements were made to allow Governments to 
obtain duplicates of the international standard. 
lor this purpose the Austrian Government gener- 
ously offered to provide the radium required at 
a considerable reduction in price. It was 
arranged that duplicate standards should be 
prepared and tested in Vienna in terms of their 
secondary standard, and then sent on to Paris 
to be tested again in terms of the international 
standard. In all six duplicate standards have 
NO. 2301, VOL. 92| 
NATURE 
be in Pea ahiy good agreement. 
parisons of the quantities of radium is made | 
means of the penetrating y rays, and it is” 
Striking testimony to the accuracy of this meth 
that the independent measurements have agreed 
so closely, ee widely differing oe 
places. 
It will be remembered that Dr. Beilby, F.R. Sif 
very generously defrayed to Mme. Curie the cost — 
of the radium forming the international standard, 
and thus relieved the International Committee of 
the necessity of collecting special funds for this — 
purpose. Immediately after the fixing of the 
international standard, arrangements were made 
in this country to obtain a duplicate standard to 
be placed in charge of the National Physical 
Laboratory at Teddington. Dr. Beilby again 
stepped in in a very generous manner and 
agreed to defray the expense of acquiring the 
British radium standard, which was delivered to 
the National Physical Laboratory a few months 
ago. The British radium standard does not differ 
much in radium content from the international 
standard, containing about 20 milligrams of pure 
radium chloride. 
A circular has now been issued by the National _ 
Physical Laboratory, stating that they are pre- 
pared to standardise preparations of radium and 
mesothorium in terms of the international 
standard, and a detailed list of testing charges 
has been issued. In the beginning, the Labora- 
tory has very wisely confined itself to undertaking — 
the standardisation of strong preparations of | 
radium and mesothorium only. The comparison 
with the British standard will be made by y ray 
methods. Tests on radio-active minerals, radio- 
active waters and other materials of weak activity, 
will not be undertaken at the moment, though, 
no doubt, arrangements will be made as the new 
radio-active department progresses to undertake 
some work of this character in the future. The 
Laboratory sends. out a certificate that the active 
material under examination shows a y ray ac- 
tivity equivalent to a certain weight of metallic 
radium, but no guarantee is given of whether 
the activity is due to radium itself, for it is well 
known that it is not easy to distinguish without 
special tests between preparations of radium and 
mesothorium. Preparations of the latter are 
standardised by expressing their y ray activity 
at the time of testing in terms of a definite weight 
of metallic radium in radio-active equilibrium. 
Both the Reichsanstalt and the National Physical 
Laboratory express the activity of their pre- 
parations in terms of metallic radium, and not in 
terms of bromide or chloride. This appears to me 
a very wise step, for it is obviously more definite 
and scientific to express the results in this 
form. It is also very desirable that all radium 
should be bought and sold in terms of metallic 
radium, thus avoiding the uncertainty that some- 
