APRIL 25, 1907 | 
NATURE 
605 
ing any adequate recognition of the work which in 
later days caused his name to be handed down to 
posterity. 
Of the remaining two books on our list a great 
deal might be said, but it would be difficult to give 
more than a bare statement of their contents in a 
general review of the present character. 
development of the theory of algebraic functions by 
algebraic methods occupies a useful place in the litera- 
ture of the subject, and is well adapted for use as an 
introductory treatise. In the matter of exposition, the 
summaries at the commencement of each chapter are 
valuable. The subject-matter includes a discussion of 
the Riemann-Roch theorem, Pliicker’s formula, and 
the Abelian integrals. The development of the 
theory, which is applicable to algebraic equations of 
the most general character, culminates in the com- 
plementary theorem, from which such applications as 
those just mentioned follow as corollaries. 
Prof. Duhem’s treatise has for its object the study 
and analytical expression of the equations of a 
material medium for displacements and stresses of 
a more general character than those considered in 
the ordinary analysis of stresses and small strains. It 
thus takes account of finite strains and of viscous in 
addition to elastic resistances. It includes the study 
of isothermal and adiabatic changes. The problem of 
wave propagation is discussed at considerable length, 
and in particular the conditions for permanence of 
wave motion. Hysteresis is not talken into account. 
The problem is a generalisation of that dealt with in 
1874 by Dr. Oskar Emil Meyer. Some time back a 
small elementary treatise was reviewed in NaTURE 
dealing with a somewhat cognate subject, namely, 
the classification of the various phenomena that can 
exist in a deformable medium, and the present treatise 
may be conveniently described as an analytical dis- 
cussion of the x, y, and z equations, while the little 
book in question explained the A, B, C of the subject. 
Gao B: 
OUR BOOK SHELF. 
Arboriculture Fruitiéve. By Léon Bussard and 
Georges Duval. Pp. xii+562; illustrated. (Paris: 
Bailliére et Fils, 1907.) 
Tue object of this little book, we are told, is to be 
useful to fruit-growers, and with that view to lay 
before the reader in a condensed but systematic form 
as complete a general view as possible of the scien- 
tific principles underlying practical methods of fruit 
culture. 
The actual details of cultivation do not differ 
materially from those followed in this country, but 
there is a marked difference in the manner, and 
especially in the spirit, in which the several oper- 
ations are carried out in the two countries. 
Here the details of pruning, pinching, and the like 
are done in routine fashion, handed down from our 
predecessors and pursued because experience has 
shown the utility of the practice. 
In France much more thought is given to the 
matter. The book before us affords an instance of 
this. The various shapes and positions which the 
NO. 1956, VOL. 75. 
Dr. Field’s | 
buds assume and the circumstances in which they 
are formed are gone into with much detail, and we 
have descriptions of lambourdes, dards, brindilles, 
cochonnets, bouquets de mat, chiffons, couwrsons, and 
bourses, for many of which we have no correspond- 
ing terms in English. Nevertheless, a knowledge of 
these details is essential to a rational system of 
pruning, and apart from their practical interest they 
should be carefully studied by those interested in 
bud-variation and *‘‘ mutation.”’ 
We do not think that botanists in general 
adequately recognise the great diversity that exists 
in the buds of a single tree. The study of a pear- 
branch or of a peach-shoot would form an excellent 
preliminary exercise to the investigation of bud- 
variation, and perhaps serve to restrain premature 
theoretical pronouncements. For this reason, apart 
from its practical utility, we can commend the work 
before us as well thought out and carefully written. 
The principal varieties are described, the illustrations 
are appropriate, there is a table of contents, and an 
index, the latter not so complete as it should have 
been. 
Physikalische Kristallographie vom Standpunkt der 
Strukturtheorie. By Ernst Sommerfeldt. — Pp. 
vit132. (Leipzig: C. Tauchnitz, 1907.) Price 
6 marks. 
Tue title of this book is somewhat misleading. Ac- 
cording to the commonly accepted nomenclature of 
crystallography the book would be described as a 
geometrical account of the structure-theory with a 
few physical applications. The ground covered is 
hardly wide enough to warrant the name ‘‘ physical 
crystallography.”’ 
The author’s style and method are obviously 
modelled on those of Sohncke. His account of the 
230 possible types of crystal-structure is descriptive 
rather than logical, and will appeal far more to a 
practical crystallographer who wishes to have some 
slight acquaintance with modern developments of the 
structure-theory than to a mathematician who re- 
gards the subject as an application of the group- 
theory. The latter will probably feel a little irritated 
at the absence of exactness in definition and com- 
pleteness in proof. For instance, the “*space- 
partitions’? on which the argument is based are 
nowhere clearly defined, and the reason given (p. 65) 
for assuming fifteen of these partitions as funda- 
mental is quite unconvincing. Surely the partitions 
should either b= limited to the fourteen possible space- 
lattices or be extended to include such figures as 
Kelvin’s fourteen-walled cell. Sohncke’s systems are 
illustrated by photographs of excellent models, but 
such diagrams probably convey very little to a reader 
unless they are arranged for stereoscopic use. The 
author gives, however, figures showing the projec- 
tions of these models on a plane, which will doubtless 
be an assistance to the student, though they might 
with advantage be clearer. 
The last forty pages of the book are devoted to a 
discussion of some physical applications of the 
structure-theory. Here the author appears at his 
best, and has some very interesting things to say on 
the subiect of etched figures and rotatory polarisation. 
His suggestions on etching of low symmetry seem to 
be new; those on rotatory structure, twinning, &c., 
are to be found in other books, but the author has 
brought the argument well up to date. ~All this part 
of the treatise is well worth reading, except that in 
the chapter on crystals with a trigonal axis the real 
point at issue is a little obscured. 
1B le lala 
