May 19, 1923] 
NATURE 663 
o 

nucleus is rotating with the arms. Now, this motion is 
just what Jeans deduced from theoretical considera- 
‘tions, taking into account the viscosity of the mass. 
_ The time of rotation of the nebula, and the velocities 
found spectroscopically, together give an estimate of 
the distance of the nebula M. 33 as 2000 parsecs, and of 
‘its diameter as 30 parsecs. The mass of the whole is 
about 100,000 times that of the sun. The nebula in 
_ Andromeda probably has a mass 20,000,000 times that 
of the sun. 
The velocity of the arms of M. 33 is such that the 
whole of the visible matter must have been within the 
nucleus 200,000 years ago; and as we must suppose 
_ that the nebula is older than this, matter must be 
continually ejected. Jeans gives strong ground for 
believing that it condenses to form stars of mass 
comparable with the sun. 
The method of rupture of much denser and smaller 
masses is next considered. Jeans has already shown 
that a star will break up into two fragments com- 
parable in mass if it rotates sufficiently rapidly. Some 
_ double stars show such light variations and velocities in 
the line of sight as indicate that they are in close 
contact, agreeing with the hypothesis that they have 
just been formed by the fission of a single star through 
excessive rotation. Their periods of revolution and their 
' spectral type (B) agree with further predictions of the 
theory. In some cases a stationary calcium atmosphere 
surrounds both components ; this is readily explicable 
as the original atmosphere of the star, which has not 
yet attached itself to either component, but will divide 
into two when the components get far enough apart. 
The last few pages give a short summary of the tidal 
theory of the origin of the solar system. The dis- 
ruption of the sun by the tidal action of a passing star 
is supposed to have led to the formation of the planets. 
Jeans considers that such an event may have happened 
to some other stars, but that these constitute only a 
small fraction of the stars we know. The majority 
of the stars are probably unattended by planets, and 
perhaps the earth is the only body in the universe 
capable of supporting life. 
HAROLD JEFFREYS. 
. 

Military Mining. 
The Work of the Royal Engineers in the European War, 
1914-19. Military Mining. (Published by the 
Secretary, Institution of Royal Engineers, Chatham.) 
Pp. x+148+6r plates. (Chatham: W. and J. 
Mackay and Co., Ltd., 1922.) 12s. 6d. (7s. 6d. to 
members of the I.R.E.) 
HE volume before us describes a most arduous 
branch of the work that the Royal Engineers 
were called upon to carry out in the War—a branch, the 
NO. 2794, VOL, 111] 

final success of which was largely due to the technical 
skill of civilian coal-miners from Great Britain working 
under mining engineers from the Colonies and abroad. 
The book is divided into three sections dealing 
with (x) the history of mining during the major opera- 
tions of the campaign, (2) mine rescue work, and (3) 
technical considerations. 
At the end of the first battle of Ypres “ the study 
and practice of military mining were suddenly revived 
by the discovery that stationary trench systems 
brought back all the old features of fortress warfare.” 
Before the end of 1914 at least two mines were ex- 
ploded by the enemy under our trenches. This caused 
a demand for special mining units, and in February 
1915 the first party of British miners arrived in France. 
By the end of June 1916, operations had extended so 
much that a total force of 25,000 men was employed 
in this work, and during that month no less than 227 
mines were blown on the British front, ror by us and 
126 by the Germans. 
The greatest of many successful mining achieve- 
ments during the war was the deep-level attack at 
Messines on June 7, 1917, when on a narrow front 
and in the space of 30 seconds mines were fired con- 
taining nearly 1,000,000 lbs. of high explosive. ‘“ The 
moral effect of these explosions was simply stagger- 
ing,” writes General Ludendorff in his Memoirs, and 
he attributes to them the success of our attack. This 
scheme was remarkable also for the long period of 
preparation (it was begun in the previous summer) 
and the consequent anxiety lest its extent should 
become known to the enemy. A month before the 
attack they were clearly heard in deep workings at 
Hill 60, but it was correctly calculated that their 
gallery would just pass clear over ours, and they were 
allowed to go on working. 
In addition to offensive mining an immense amount 
of work was done by tunnelling companies in the 
construction of dug-outs, communication tunnels, 
and road repair, and during the summer of 1918 in 
the removal of mines and traps left by the enemy 
as they retired. 
Owing to the number of casualties in the early days 
of mining, chiefly caused by carbon monoxide from the 
detonation of high explosives, rescue work became of 
great importance, and was effectively organised under 
Lieut.-Col. D. Dale Logan. The next step was the 
formation in 1916 of a special medical service for 
tunnelling companies, all the officers of which had 
been for years in mining practice. A well-deserved 
tribute is paid to the work of these officers and of the 
rescue men, whom it was found necessary to select 
with the greatest care owing to the very trying nature 
of their work. 
