230 
NATURE 
[JANUARY 3, 1907 
speed of 15 metres per second, or 54 kilometres per hour, 
can be maintained for sixty hours with the quantity of 
benzene the machine will carry. With one motor alone 
working a speed of 11 metres per second would be main- 
tained for 120 hours. The advantages of the Zeppelin air- 
ship are more or less counterbalanced by the present 
mecessity of using a sheet of water for starting and land- 
ing. Apart from the uses of such a machine in warfare, 
its applications in time of peace to the meteorological 
survey of the atmosphere are contemplated. 
AN interesting but highly mathematical memoir by Prof. 
Karl Pearson and Mr. J. Blakeman on ‘‘ A Mathematical 
Theory of Random Migration’’ has just been issued by 
Messrs. Dulau and Co. (Drapers’ Co. research memoirs, 
biometric series, iii.). The problem dealt with is, in 
simple terms, the following :—given that a large number 
of individuals move by successive straight steps of length /] 
in random directions, starting from one and the same 
point, required to find their distribution after n such steps. 
The solution, which is obtained in terms of Bessel func- 
tions, is applicable to such practical problems as the in- 
filtration of mosquitoes into a cleared area, or the recovery 
of a habitat by a species which has been driven out owing 
to temporarily unfavourable conditions. Prof. Pearson 
obtained some assistance in the solution of the problem 
through a letter addressed to our correspondence columns 
(vol. Ixxii., p. 294, July 27, 1905); Lord Rayleigh directed 
his attention (ibid., p. 318) to the fact that when the 
number of steps n is very large, the problem becomes 
identical with a problem in sound; and Prof. Kluyver pre- 
sented a memoir on the subject to the Royal Academy of 
Sciences of Amsterdam (Proceedings, October 25, 1905). 
Reference should, we think, have been made, in the intro- 
duction to the memoir, to the address delivered by Major 
Ross ‘On the Logical Basis of the Sanitary Policy of 
Mosquito Reduction’ at the St. Louis Congress of 1904 
(British Medical Journal, May 13, 1905). This contains 
the first published discussion of the problem, with especial 
reference to its most important practical application, and 
suggests a simple approximate solution in terms of the 
binomial series. 
AN investigation of the temperatures obtainable by the 
use of solid carbon dioxide under different pressures forms 
the subject of a paper by Messrs. John Zeleny and Anthony 
Zeleny in the Physical Review (vol. xxiii., No. 4). Ina 
deep vessel of such a shape that the material is surrounded 
by its own vapour, the same temperature is given under 
any one pressure by the carbon dioxide either alone or 
when mixed with alcohol or ether; it is, however, more 
easy to maintain the temperature constant when the solid 
is moistened with ether. A table is given showing the 
temperatures obtainable by varying the pressure above the 
solid from 2 cm. to 84 cm. of mercury. At the former 
pressure the temperature is —116°-7, and at the latter 
Sap? (Ce 
SomE very remarkable results have been obtained by 
Prof. R. W. Wood in the course of an investigation of the 
fluorescence and magnetic rotation spectra of sodium 
vapour, published in the Proceedings of the American 
Academy of Arts and Sciences (wol. xlii., No. 13), and also 
in the Physikalische Zeitschrift (No. 24). The fluorescence 
spectra were observed using monochromatic light of a 
definite wave-length as source of excitation. Different 
series of lines are seen with different exciting wave-lengths. 
The series are mostly of a very simple character, consist- 
ing of groups of lines separated by a constant wave-length. 
The same series of lines are also observed in the magnetic 
NO. 1940, VOL. 75] 
rotation spectrum of sodium vapour, which can thus be 
subjected to analysis. Certain lines, however, which occur 
singly in the magnetic spectrum occur as doublets in the 
fluorescence spectra. The detailed measurements obtained, 
from the comparative simplicity of the phenomena, are 
likely to prove of very great importance in discussing the 
mechanism of molecular vibration and radiation. 
From the dissociation theory of solution it might be 
inferred that as the radiation from a radio-active substance 
renders a gas conducting by causing ionisation of the 
gaseous particles, an increase of the conductivity of aqueous 
solutions should follow from their exposure to radio-active 
influence. The effect in the latter case should, indeed, be 
very marked, inasmuch as partial ionisation of a salt 
occurs merely on dissolving it in water, whereas in the 
case of a gas ionisation takes place only under special 
influences. The conductivity of a large number of salts 
in aqueous solution has been measured by M. S. M. Sabat 
(Bulletin of the Cracow Academy of Sciences, 1906, No. 1) 
during their exposure to the radiation produced by 0-2 gram 
of Prof. Curie’s most active preparation of radium bromide. 
After making allowance for the alteration of resistance 
caused by the rise of temperature due to the radiation, the 
conclusion is drawn that not the slightest change in con- 
ductivity can be attributed to a change in the degree of 
ionisation of the salt within the solution. If such a change 
of ionisation takes place it is so slight as to be altogether 
negligible. ‘ 
Mr. Davin Nutt has published for the Folk-lore Society 
a ‘‘ bibliography of Follx-lore ’’ for 1905, which has been 
compiled by Mr. N. W. Thomas. The price of the booklet 
is rs. net. 
Messrs. J. anp A. Cuurcuitt have published a third 
edition of ‘‘ A Handbook of Physics and Chemistry adapted 
to the Requirements of the First Examination of the Con- 
joint Examining Board of the Royal Colleges of Physicians 
and Surgeons and also for General Use,’’ by Messrs. 
Herbert E. Corbin and Archibald M. Stewart. 
We have received a copy of the report of the Meteor- 
ological Service of Canada for the year ended on 
December 31, 1904. In nearly four hundred foolscap pages 
Mr. R. F. Stupart, the director, has brought together 
results of observations of the temperature, pressure, rain- 
fall, snowfall, amount of bright sunshine, and other meteor- 
ological data concerning all parts of Canada. The volume 
also includes the magnetic results for each month and for 
the year 1904. 
In his work ‘‘ Erkenntniss und Irrtum,’? reviewed in 
Nature of November 30, 1905 (vol. Ixxiii., Supp., p. vii), 
Prof. E. Mach partly included three essays in which the 
questions of the nature, origin, and development of our 
concepts of space were discussed from several points of 
view. The English rendering of these essays, which 
originally appeared in the Monist, has now been published 
in volume form by Messrs. Kegan Paul and Co., Ltd., 
under the title “‘Space and Geometry in the Light of 
Physiological, Psychological, and Physical Inquiry.’ 
In Nature of October 11, 1906 (vol. Ixxiv., p. 594), 
reference was made to a paper by Prof. Kamerlingh Onnes 
and Dr. Heuse on the expansion of glass at very low 
temperatures, and attention was directed to the work of 
Dr. Travers on the same subject. Prof. Onnes writes to 
point out that the memoir referred to was a translation of 
a Dutch paper, published somewhat earlier than that of 
Dr. Travers, to which we alluded, and that in a more 
recent communication on the same subject he has not failed 
to recognise the results obtained by this investigator. 
