APRIL 12, 1901.] 
most difficult problems that the study of the 
origin of coal and other fossil combustibles 
presents. It should be carefully studied from 
that point of view. 
Neither should the fact be left unstated that 
in these difficult and recondite researches M. 
Renault has advanced theories that are not 
accepted by all, but the criticism and, if need 
be, the disproof of which belongs to those who 
are engaged in the same line of investigation 
and are equipped for such a task. 
Lester F. WARD. 
The Elements of Astronomy. By Sir ROBERT 
Batu. New York, The Macmillan Company. 
1900. 183 pages, 23 figs., and 11 full-page 
plates. Price, 80 cents. 
This little book contains a clearly written 
account of astronomical subjects, adapted to 
the needs of beginners. After a brief historical 
introduction and an explanation of the ap- 
parent diurnal motion of the celestial sphere, 
the Sun, as the heavenly body most important 
to us and most interesting to the novice, is 
rightly placed first. If any change were to 
be suggested here, it would be that this topic 
should receive fuller treatment and more com- 
plete illustration. The author’s admirable 
Story of the Sun, which is both accurate and 
interesting, fits him to present this subject ad- 
' vantageously. 
It is to be regretted that the eclipse photo- 
graphs, which are supposed to show solar 
prominences and the corona, are so badly 
reproduced as to be almost worthless; and 
while the introduction of photographic illus- 
trations directly from nature is very desirable, 
the public has a right to demand that such 
pictures in a work of more than ephemeral 
value shall have that degree of precision which 
modern art processes are able to give. Incase 
the publishers have not at their command 
facilities for reproducing pictures with delicate 
details, a well-executed engraving, correctly 
interpreting such details, is to be preferred toa 
poor photograph. Good illustrations are given 
of the Full Moon, Saturn, Jupiter, the Dumb- 
bell Nebula, and clusters in Hercules and in 
Perseus. 
Since one of the objects of scientific study is 
SCIENCE. 
581 
to inculcate conceptions of precision, the indis- 
criminate grouping of stars of several orders of 
magnitude from Sirius (—1.5 mag.) to Capella 
(0 mag.) under the title ‘ first magnitude’ stars 
(p. 7-8) is to be deprecated. 
In an edition prepared for American readers 
it might be well, if a common name is to be 
used, to substitute The Dipper for The Plough 
in designating a part of Ursa Major which ‘in 
this country ’ is familiarly known by the former 
title. 
A similar remark applies to the statement on 
p. 57 that midsummer twilight in ‘our’ lati- 
tudes lasts all through the night, which lacks 
generality and is inappropriate in a science 
whose chief merit as a discipline for young 
readers is that it tends to broaden our con- 
ceptions by wiping out local distinctions. 
The author’s familiarity with mathematical 
processes gives him a firm grasp on everything 
of a geometrical nature, but also a beautiful 
simplicity and directness in his demonstrations, 
which does not always follow from individual 
comprehension. The chapter on the diurnal 
motion is simplified by the omission of some 
details which would have to be considered in a 
more extended treatise; but one cannot omit 
to note that quite apart from this, the method 
and language of the demonstration are uncom- 
monly clear and convincing. 
It is natural that we should expect the same 
clearness in those subjects which Sir Robert 
Ball has made peculiarly his own—such as pre- 
cession and the tides—and the reader will not 
be disappointed here. The history of the Harth- 
Moon system and the chapter on gravitation 
will be found especially interesting. 
It is permissible, even in an elementary 
treatise, that an author should develop some- 
what those parts of the subject on which he is 
an authority and where he can speak better 
than any one else ; and since a selection has to 
be made in a small work like this, it is just as 
well that the illustrations chosen should be 
those most familiar to the author; but there 
are other inequalities which cannot be com- 
mended. 
A considerable space is devoted to an argu- 
ment as to the exceedingly high surface-tem- 
perature of Jupiter, which is purely speculative, 
