January 14, 1904] 
NATURE 
247 
LETTERS TO THE EDITOR. 
[Vhe 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.] 
Radio-active Gas in Mineral Springs. 
In a letter to Nature of August 13, 1903, it was 
announced that experiments carried out at the Blythswood 
Laboratory had shown the presence of a radio-active con- 
stituent in the gases derived from the mineral waters of 
Bath. An account of our further investigations has been 
given in a paper read before the Royal Philosophical Society 
of Glasgow, November 18, 1903. Samples of water from 
the Buxton springs have been tested with results exactly 
similar in character to those given by Bath waters. In 
both cases the ionisation-current through the gas obtained 
from the water increased to a maximum in about one hour 
from the commencement of an experiment, and then 
diminished to the normal value. In a note added to this 
paper, December 15, 1903, an experiment is described 
similar to one carried out by Mr. E. P. Adams (Phil. Mag., 
vol. vi. p. 563, 1903). A current of air was drawn through 
a very dilute solution of a radium salt, and then through a 
Winchester quart containing distilled water. The air 
current was continued for two hours. ‘The distilled water 
after this treatment was tested in exactly the same manner 
as the Bath water, ‘‘ the results being in all respects similar. 
. . . It is therefore probable that the radio-activity of these 
(mineral) waters is due to the presence of radium near their 
source.” 
This anticipation has been confirmed by the Hon. R. J. 
Strutt’s discovery of radium in the iron deposits left by 
the hot springs of Bath. 
We have recently obtained conclusive evidence of the | 
presence of radium emanation in the Buxton springs 
through the kindness of Mr. J. W. Wardley, who has 
collected samples of the gases that rise through the water 
and forwarded them to us for examinatien. In our former 
experiments with water sent from the springs the amount | 
of gas obtained was extremely small, and the consequent 
activity inconsiderable. We now find that the activity of 
the gas falls to half value in about three and a half days, 
the corresponding time for the radium emanation being 
3:71 days (Rutherford). 
It would be interesting to know whether treatment by 
the gases obtained from the springs possesses any thera- 
peutic value. BLYTHS WOOD. 
H. S. ALLEN. 
Blythswood Laboratory, Renfrew. 
Projection of Imitation Spinthariscope Appearance. 
In thinking over how to exhibit to an audience the appear- 
ance of a zinc-sulphide screen bombarded by radium, one 
of my sons suggested that a kinematograph film often 
imitated the effect, by reason of its punctures being thrown 
on the screen by intermittent light. Accordingly he made 
a model with two numerously punctured plates mounted on 
eccentrics so as to slide over one another in a_ periodic 
fashion. It is sufficient, however, to hold two punctured 
plates by hand in the place of a lantern slide, and move 
them irregularly over each other slowly. 
Ouiver Lopce. 
American Tropical Laboratory. 
Tue Director of Kew presents his compliments to the 
Editor of Nature and requests the publication of the en- 
closed letter. 
Kew, January 8. 
New York Botanical Garden, 
Bronx Park, New York City, 
December 26, 1903. 
My dear Sir William, 
Referring to my letter of August 14, 1903, I take pleasure 
in stating that the group of buildings of the Colonial 
Government of Jamaica at the Cinchona Botanical Garden | 
NO. 1785. VOL. 69] 
will be maintained as a botanical laboratory by the New 
York Botanical Garden under an agreement with the 
Colonial Government, and with the cooperation of the De- 
partment of Public Gardens and Plantations of Jamaica; 
sufficient land for experimental purposes and for a nursery 
is included in the leasehold privileges. The buildings in- 
clude a residence known as Bellevue House, three labor- 
atories, two ranges of glass, and one or two small buildings 
suitable for lodgings. 
Investigators are offered the following facilities :— 
(1) The use of tables in the laboratory buildings. 
(2) Lodging in Bellevue House or in one of the other 
buildings at Cinchona. 
(3) The use of land for experimental purposes. 
(4) Privileges to study the plantations at Cinchona, and 
also those at Hope and Castleton Gardens. 
(5) Privilege to consult the botanical library of the De- 
partment of Public Gardens and Plantations at Hope 
Gardens, and to take books therefrom to Cinchona under 
such conditions as may be imposed by the Director of Public 
Gardens and Plantations. 
(6) An immense number of indigenous species are within 
easy reach in the primitive forests adjacent to Cinchona, 
All persons who may apply for permission to study at 
Cinchona must submit such evidence as the Director-in- 
Chief of the New York Botanical Garden may require that 
they are competent to pursue investigation to advantage. 
While in residence at Cinchona they will be under the super- 
vision of the Hon. William Fawcett, Director of Public 
Gardens and Plantations, to whose interest and advice the 
establishment of this American tropical laboratory is largely 
due. 
A laboratory fee, payable to the New York Botanical 
Garden, will be required of persons granted the above 
privileges. 
Upon approval by the scientific directors of the New 
York Botanical Garden, any other institution, society or 
individual may be assigned the use of a table at Cinchona 
by the payment of one hundred dollars annually, which will 
entitle them to nominate students desiring to avail them- 
selves of the facilities of the laboratory for admission with- 
out the payment of fees, but not more than one person may 
be granted the use of any table at the same time. 
The necessary expenses for a month’s residence at 
Cinchona, including travelling expenses to and from ports 
on the Atlantic seaboard of the United States, are from 
140 dollars to 200 dollars; for two months’ residence 160 
dollars to 230 dollars. 
Dr. MacDougal will be glad to give you any further in- 
formation concerning this subject that you may care for, 
and we hope that you or some of your students may be able 
to utilise the resources of the laboratory from time to time. 
Yours sincerely, 
(Signed) N. L. Britton, 
Director-in-Chief. 
Escape of Gases from Atmospheres. 
In the Literary Supplement of the Times of December 25, 
1903, an erroneous statement is on p. 375 placed before its 
readers, to the effect that our alleged knowledge of the 
escape of some gases from the atmospheres of planets and 
satellites is based on an assumed absence of helium from 
the earth’s atmosphere, and has been disposed of by the 
discovery that helium is present. A brief letter was 
addressed to the editor of the Times giving proofs that the 
above statement is incorrect, and from this letter an extract 
has been published as a note in the next number of the 
Literary Supplement. The matter concerns one of the great 
cosmical agencies of nature, and I therefore request you to 
allow me to deal with the subject in the more adequate way 
which is permissible when addressing a scientific journal. 
The problem of the escape of gases from atmospheres has 
been approached in two ways, both of which the present 
writer has tried, and one of them has also of recent years 
been attempted by other scientific men :—(1) The problem 
has been treated deductively by ascertaining the law of the 
distribution of speeds among the particles of a hypothetical 
kinetic system, so constructed as to be a model of gas simple 
enough for human mathematics to enable us to compute 
the distribution of speeds within it, and which it was hoped 
