——- ee Sa 
JuNE 20, 1912] 
sphere has been left out of account. He describes 
an apparatus used for testing the degree of inflamma- 
bility of coal dusts in different atmospheres, and 
proves the importance of the percentage of oxygen. 
Thus a certain coal dust gave no ignition in an atmo- 
sphere containing 18 per cent. of oxygen, partial 
ignition with 184 per cent., and full ignition with 
Ig per cent. of oxygen. The results are suggestive, 
and are applied by the author to explain the con- 
tradictory results obtained by previous workers on 
the same subject. In particular, it is pointed out that 
a given coal dust can only be tested as to safety when 
in presence of air of the same composition as that 
of the mine. Dr. Harger suggests that if an atmo- 
sphere containing 173 per cent. of oxygen could be 
supplied to mines coal dust ignitions would be ren- 
dered impossible, and explosions of any kind quite 
out of the question. He holds that such an atmo- 
sphere would be quite as good for respiration. Prac- 
tically, an atmosphere containing 19 to 19} per cent. 
of oxygen and # to 1 per cent. of carbon dioxide 
would suffice for the majority of mines. 
Engineering for June 14 contains an illustrated 
description of a ferro-concrete sludge-pumping pontoon 
for the Manchester Ship Canal. The pontoon 
measures 100 ft. long by 28 ft. wide by 8'5 ft. deep 
from the keel to the main deck, and is the first 
example of a ferro-concrete vessel in this country. 
The designs, on the Hennebique system, are the work 
of Messrs. L. G. Mouchel and Partners, Westmin- 
ster. Reasons for the selection of ferro-concrete con- 
struction were lower initial cost, elimination of main- 
tenance charges, and readiness of repair., There are 
four transverse and two longitudinal watertight buik- 
heads, thus amply providing for the security of the 
vessel. The work of construction was commenced in 
August last, and all ferro-concrete work was com- 
pleted on March 9. The water-tight compartments 
have since been tested by filling with water. The 
‘pontoon is now ready for launching, an operation 
which will take place in the course of a few days. 
We have before us a number of attractive little 
volumes, in which many branches and aspects of 
science are successfully surveyed. The books belong 
to three distinct series, namely :—(1) Manuals of Science 
and Literature, published by the Cambridge Univer- 
sity Press, at 1s. net a volume; (2) The Home Uni- 
versity Library of Modern Knowledge, published by 
Messrs. Williams and Norgate, at the same price; 
and (3) The People’s Books, published by Messrs. 
T. C. and E. C. Jack, at 6d. net each. Some of the 
volumes in the first two series have been noticed 
separately in our review columns, and they may be 
regarded as typical of the rest. The Cambridge 
books are mostly too technical for general readers, 
but for students who have some acquaintance with | 
the subjects with which they deal, they are admir- 
able. The books in the Home University Library 
are somewhat more popular, and are all on a high 
level of exceilence. The People’s Books represent an 
independent and significant venture, which we cor- 
dially hope will meet with success. In this series 
we are provided for the modest sum of sixpence each 
NO. 2225, VOL. 89] 
NATURE 
407 
with dainty volumes of about ninety-six pages, written 
by people whose lives have been devoted to the sub- 
jects which they survey. With such an abundance of 
accurate and authoritative knowledge available, every- 
one who desires can be put into touch with the present 
position of fact and opinion upon all scientific sub- 
jects of outstanding importance. Whatever demand 
exists for cheap books upon the various departments 
of natural knowledge is satisfactorily met by the 
volumes in this series, and we trust the enterprise of 
the publishers will meet with decided success. That 
there should be three comprehensive series of more or 
less popular books in which the volumes dealing with 
branches of science are written by men and women 
of distinction may, we hope, be taken as an indica- 
tion of increased interest in scientific work. 
Messrs. JOHN WHELDON AND Co., 38 Great Queen 
Street, Kingsway, W.C., have just issued a classified 
zoological catalogue, comprising faunas of all coun- 
tries, and including extensive collections of works on 
ornithology, mammalia, reptilia, fish and fisheries and 
general zoology. 
OUR ASTRONOMICAL COLUMN. 
CONSTITUTION OF THE Mitky Way.—At this epoch 
when many theories as to the construction of our 
universe are being propounded, the collection and 
correlation of the available data is a labour of great 
value, and such works as Prof. Charlier’s ‘‘ Studies in 
Stellar Statistics ’’ become invaluable. 
His first memoir, appearing as No. 8 of the Meddel- 
anden fran Lunds Astronomiska Observatorium, deals 
with the constitution of the Milky Way, and although 
not generally suitable for popular treatment, contains 
a very striking exposition of the difficulties which 
beset the investigator, chiefly because the data are, 
as yet, so few. In this memoir he deals with the 
number of stars in different parts of the galaxy, and 
the distribution of their luminosities; subsequent 
memoirs will deal with the problems from other points 
of view. Dividing the sky into forty-eight squares of 
equal area, he finds inter alia that a certain square in 
the Milky Way contains between 30,000,000 and 
250,000,000 stars, while in a square containing the 
pole of the Milky Way the corresponding limits are 
600,000 and 2,000,000. The wide limits well illus- 
trate the uncertainty produced by the paucity of the 
data available. Similarly, Prof. Charlier finds that 
the limiting distance of our stellar system, in the 
direction of the plane of the Milky Way, may be put 
between 600 and 1400 ‘‘siriometers,”’ the “‘ siriometer ”’ 
being a distance equal to a million times the sun’s 
mean distance from the earth. 
Tue Sorar Ecuipse or Apri 17.—The current 
number (53-54) of the Gazette Astronomique contains 
a large number of observations of the solar eclipse 
of April 17, made by the various parties organised 
by the energetic astronomical society of Antwerp to 
observe at Silenrieux, in the province of Namur. The 
results show that the central line passed exceedingly 
close to, or over, Silenrieux. A memoir embodying 
the complete results of the observations and their dis- 
cussion is being prepared for publication by the society. 
Other important results are published in L’Astro- 
nomie for June, and are illustrated by many interest- 
ing diagrams and photographs. Among the latter 
are three by M. Rudaux, who observed in the Pyre- 
nees, the first showing the dark moon projected on 
the lower corona beyond the northern cusp of the 
