662 
NATURE 
[AUGUST 27, 1914 
tame to find the classification of both cystoidea and (7) Dynamics. By -Prof2 H.; Lambs Pp.) xi 
blastoidea following that of Bather. For the 
crinoidea, however, Dr. Springer naturally takes, 
with some modification, the main divisions estab- 
lished by Wachsmuth and Springer. The post- 
paleozoic genera are separated as an _ order, 
articulata, which seems rather a backward step; 
but it is interesting to have them arranged ac- 
cording to the views of Dr. A. H. Clark, even 
though much space is given to purely recent 
forms. Dr. H. L. Clark, who revises the aster- 
ozoa, seems timorous by contrast. Dr Kaas 
Jackson (whose help throughout the editor ac- 
knowledges) has fortunately been able to deal 
with the echinoidea on the lines of his recent great 
monograph; our only regret is that the name 
centrechinoida (vice diademoida) has thus entered 
on its text-book career. 
In the bryozoa, and in mollusca other than am- 
monoidea, we detect no great change; that impor- 
tant order has been entrusted to Prof J. Perrin 
Smith, who strikes a happy mean between the 
phylogenists and the geologists. With such re- 
visers-as Drs. C. D. Walcott, J.:M. Clarke, P. E. 
Raymond, A. Petrunkevitch, W. T. Calman, and 
A. Handlirsch, the chapter on the arthropoda 
proves sound and up-to-date. The editor must 
have felt very happy when he had seen its last 
page through the press, and could turn to compile 
the index of more than 5500 names. We offer 
our congratulations and thanks. 
MATHEMATICAL TEXT-BOOKS. 
(le Hasord: by, Prot. “EE.” Borel: -) Pp. ‘ive- 
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By bte. burner and ror. |. mm. Bose.” Pp. 
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(3) A Junior Trigonometry. By W. G. Borchardt 
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(1) JT has been said that “Chance is the 
measure of our ignorance,” and if by this 
it is meant that any event, the causes of which we 
do not understand, is to be ascribed to chance, 
then chance is indeed a powerful factor in life; 
and many of our actions and policies are deter- 
mined by our estimate of it. The mathematical 
theory is, of course, beyond the powers of the 
ordinary reader; no one, for instance, who had 
not received a special mathematical training could 
make much of the excellent article on “ Prob- 
ability”? in the ‘Encyclopedia Britannica.” But 
there are general considerations and conclusions 
which lie apart from technical difficulties, and it 
is these that form the substance of this volume. 
The book is divided into three parts. The first 
considers the meaning of probability with illustra- 
tions from the tossing of a coin, cases of limited 
and unlimited alternatives and inverse probability ; 
examples are taken in which different methods 
appear to yield different solutions of the same 
problem, thus paving the way to an instructive 
discussion on possible elements of ambiguity in 
the data. The second part deals with the appli- 
cations of the laws of chance to sociology, 
biology, physics, astronomy, and chemistry; and 
the third with their practical and philosophical 
bearing on human affairs. All these topics should 
appeal to the general reader. 
(2) This text-book is compiled with special re- 
ference to the needs of Indian students, and 
includes all that is required by the syllabus of 
Calcutta University. There is nothing particu- 
larly original in the treatment; and although the 
importance of practical work is emphasised in 
the preface, yet in the text itself there is not as 
much as will be found in most recent English 
books. For examination purposes it will, how- 
ever, be found distinctly useful, since the book- 
work is set out clearly and there are a good 
selection of illustrative examples, worked out in 
careful detail. There is an unfortunate mistake 
in the section on circular motion, where it is 
stated that this implies the action of some force 
