876 
Agriculture in the Tropics: An Elementary Treatise. 
By Dr. J. C. Willis. (Cambridge Biological Series.) 
Third edition, revised. Pp. xvi+223+24 plates. 
(Cambridge: At the University Press, 1922.) 
12s. 6d. net. 
Dr. Wituis’s book was intended, not as a practical 
guide in field methods for the tropical agriculturist, 
but to serve mainly as an introduction to the study 
of the leading economic principles governing the 
modern practice of agriculture and planting in the 
tropics. With the remarkable developments taking 
place in tropical agriculture, such a book will require 
periodical revision to keep abreast of the times. The 
second edition was published in 1914, and the call 
for the present (third) issue has afforded a further 
opportunity for revision. It is a pity that no preface 
to the new edition has been printed, and, except for 
special information supplied by the publishers for 
the convenience of the reviewer, it would be difficult 
to trace new matter or corrections. 
No important re-arrangement of the book has been 
adopted. The four parts remain the same and the 
slight revisions made in them are neither numerous 
nor very important. There are still opportunities, 
however, for improvement in the text. In dealing 
with the West African oil-palm (Eleis guineensis) due 
reference is made to the recent planting of the palm 
in the East, but the student would gather very little 
as to the origin of the “ pericarp ” oil (not mentioned as 
such) from the account given; while the statement 
that “of late another oil has been obtained from the 
seeds of the palm” is alittle naive. Definite reference 
also should be made to the wide use of coco-nut oil for 
the manufacture of margarine. Further, as regards 
gingelly oil, while it may be true that comparatively 
little of the oil is exported from the countries of 
production, the statement should be completed by 
reference to the important export of the seed for oil 
extraction in Europe. 
The book remains, however, an excellent introduction 
to a subject of great and increasing importance, and 
should be read by all interested in the practice and 
administration of tropical agriculture and planting. 
Crystallisation of Metals: being a Course of Advanced 
Lectures in Metallurgy delivered at the Royal School 
of Mines, Imperial College, under the Auspices of 
the University of London, in February and March 
1922. By Col. N. T. Belaiew. Pp. 143+21 plates. 
(London: University of London Press, Ltd., n.d.) 
7s. 6d. net. 
CoLoneL BELarew has written a book on the “ Crystal- 
lisation of Metals,” which is remarkable in that it 
deals with the coarse structure rather than the micro- 
structure of metals. It is therefore noteworthy that 
a great many of his illustrations are natural size, while 
others are X2, 5, or 10. Only in rare instances are 
higher magnifications used, although in certain extreme 
cases remarkable pictures are given in which the 
magnification is as high as 4500. At the other extreme, 
two illustrations are given on a reduced scale (x 4) 
of Tschernoff’s famous crystal, more than fifteen inches 
in length, which was found in the upper portion of 
the pipe in the sinking head of an ingot of soft open- 
hearth steel weighing about 1oo tons. The final 
NO. 2800, VOL. 111] 
NATURE 
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[JUNE 30, 1923 
paragraphs of the book deal with the structure of 
Damascene steel, and include two beautiful illustra- 
tions, of approximately natural size, of Damascene 
blades, as well as microphotographs with an enlarge- 
ment of rooo diameters. The little book forms an 
admirable supplement to exiSting treatises on metal- 
lography, and reaches a level which entitles it toa 
place among standard works on this subject. 
Visual Illusions: their Causes, Characteristics, and 
Applications. By M. Luckiesh. Pp. ix+252. 
(London, Bombay, and Sydney : Constable and Co., 
Ltd., 1922.) 15s. net. 
In this book Mr. Luckiesh presents one hundred illus- 
trations of familiar and little-known optical illusions, 
round which the text is written. On account of the 
great complexity of the subject, the author confines 
himself to static illusions, and dispenses to a large 
extent with theory. It is inevitable that there should 
be some overlapping in any classification of visual 
illusions, since not seldom more than one factor enters 
into them ; but the arrangement or grouping together 
in the various chapters which is adopted in the book 
is a convenient and practical one. After chapters on 
the eye and vision, geometrical and depth, or distance, 
illusions are considered in detail. These are followed 
by illusions due to irradiation, colour, and lighting. 
A special chapter is added on natural illusions, such 
as the apparent size of the setting sun as compared 
with the sun at the zenith, the magnification of objects 
seen through fog, and mirage. The last four chapters 
are devoted to applications of the natural principles 
of visual illusions to practical purposes, in the shape of 
painting, decoration, architecture, and camouflage. 
The book is well written and attractively produced, 
and should be of interest to others as well as to 
students of psychology. 
Geology. By C. I. Gardiner. (Science for All Series.) 
Pp. x +138. (London: J. Murray, 1923.) 35. 6d. 
In 1914, Mr. Gardiner produced his “ Introduction 
to Geology ” (see NATURE, vol. 94, Pp. 362), in which 
he found more scope for originality than is given by 
this smaller volume. The conception of a work on 
geology “for all”” must vary with the outlook of the 
author, and Mr. Gardiner has had long experience in 
the training of beginners in the region where the 
foundations of stratigraphical geology were laid within 
the British Isles. We cannot help thinking that “all” 
would like to hear something of the Laurentian cauldro 
in which the oldest strata of Canada were immersed 
of the rich fauna of the Olenellus-beds ; of the comin: 
of the race of reptiles that was so long to dominate 
the world; and of the amazing development o 
mammals, from South Dakota and the Paris Basin to 
the Trinil river-bank in Java. But Mr. Gardine 
knows well that a fossil picked up in a Gloucestershir 
lane or from a talus in the Isle of Wight may loom 
clear, 
observations. 
