154 
WA TG Ree 
{ DECEMBER 17, 1903 
In a chapter devoted to ‘‘ our commercial policy,’’ 
the native arts are considered, such as pottery and the 
weaving of cloths. The production of these should, 
in our opinion, receive all encouragement and careful 
direction before the trading companies have ‘ im- 
proved ’’ them out of existence with their cheap Man- 
chester substitutes. Very wise, too, is Captain 
Wallis’s advice that native customs and traditions 
should be cherished, except in so far as they manifestly 
clash with the higher ideals of Christian morality. 
The question of health can hardly be avoided in a book 
on West Africa, and the author is to be congratulated 
on having grasped the main facts of the mosquito 
malarial cycle. He is aware of the danger of camping 
in a native village—the almost invariable practice— 
for, broadly speaking, it is here only that the malarial 
mosquito is dangerous, because it has been infected 
with parasites by the native children, who form, so to 
speak, the great central depdts of malarial parasites 
in Africa. In a word, the first law of health in West 
Fic. r.—Goyernment House, Bandajuma. (From “ The Advance of Our West African Empire.”’) 
Africa is efficient protection from this constant source 
of malarial fever, and a bungalow well isolated from 
native huts would mean many a European life saved. 
Our illustration of Government House, Bandajuma, 
on the contrary, shows things as they should not 
be. Those ‘‘deadly’’ huts (seen in the right-hand 
corner) mean constant danger to the European com- 
missioner, 
The book is fully illustrated, but we think many 
of the illustrations might have been chosen with greater 
care. They give but little idea of the characteristic 
scenery of the country. Thus we sought in vain for 
the magnificent cotton trees or the beautiful un- 
matched ‘‘lines’’ of the mangrove tree. We think, 
too, the title is too comprehensive for the nature of the 
book. But the author deserves our thanks for having 
given us a straightforward account of the rebellion 
and some very interesting chapters on native customs. 
We have read the book with much pleasure, and in our 
own case with an added pleasure from familiarity with 
many of the scenes and faces represented in the illus- 
trations. J. W. W. S. 
NO. 1781, VOL. 69 | 
THE IONISATION OF ATMOSPHERIC AIR. 
WheeskS ELSTER AND GEITEL have published 
an important paper in the Physikalische Zeit- 
schrift (No. 9, pp. 522-530), ‘‘ Ueber die radioaktive 
Emanation in der atmospharischen Luft.’’ They find 
that the abnormal conducting power of the stagnant 
air of cellars and caves, and the amount of induced 
radio-activity which can be obtained from such air 
upon a negatively charged rod suspended in it vary 
greatly in different regions. In some places such air 
is no more active than ordinary atmospheric air. Air 
sucked through a pipe of which one end is buried in 
the ground is generally active, like the air of most 
cellars and caves; tests of the activity of samples of 
such ground-air from different localities showed great 
variations, some being no more active than ordinary 
air. The activity of ground-air falls off at a rate com- 
parable with the rate of decay of the radium eman- 
ation. If a portion of the soil of a region in which 
the ground-air is radio-active is 
isolated, it gives to a volume of air 
in contact with it abnormal conduc- 
tivity which reaches its maximum in 
a few days. The soil retains this 
power for many months at least. 
The phenomena are all most readily 
explained by supposing that sub- 
stances, which have the power of 
producing a radio-active emanation 
like that of radium, are distributed 
in varying amount among the 
materials composing the soils of 
different regions. In the latter part 
of the paper is an account of some 
interesting observations on the de- 
pendence of the radio-activity of 
atmospheric air upon meteorological 
conditions. The increase of thé 
activity of the air which generally 
accompanies a fall of the barometer 
is attributed to the escape of ground. 
air into the atmosphere. 
Herr Himstedt repeated and con- 
firmed some of Messrs. Elster and 
Geitel’s experiments upon ground- 
air (Berichte der naturforschenden 
Gesellschaft zu Freiburg, vol. xiii. 
p- 101). In, the course of this work 
he found that air passed through a 
water air-pump acquires consider- 
able conducting power, which per- 
sists (even when the air 1s dried and filtered after pass- 
ing through the pump) for some days. He appears to 
have been unaware of the previous discovery of this 
phenomenon by Prof. J. J. Thomson. Himstedt gets 
identical results from distilled water, rain-water, and 
tap-water, whereas Thomson found distilled water and 
rain-water comparatively ineffective, the action being 
strongest with certain waters from deep wells, and 
bein attributed by him to a radio-active substance 
contained in such water. Himstedt found, as Prof. 
Thomson had previously shown, that the activity of 
the air is not removed by an electric field; he proved, 
however, that it can be removed by passing through a 
tube cooled by liquid air. He believes that water 
brought into intimate contact with a gas exerts an 
ionising action upon it. 
In the Actes de la Société helvetique des Sciences 
naturelles (85me session 1902 a Genéve), Prof. H. 
Ebert gives an account of the progress which has been 
made towards an explanation of the phenomena of 
atmospheric electricity on the ‘‘ Elektronentheorie.”’ 
He mentions some of the results of measurements, 
