JuLy 10, 1902] 
NATURE 
245 
OUR BOOK SHELF. 
The Watkins Manual of (Photographic) Exposure and 
Development. By Alfred Watkins. Pp. 124. (Here- 
ford: The Watkins Meter Co.; London: George 
Houghton and Son, 1902.) Price Is. net. 
THE author is universally known among _photo- 
graphers as the inventor of the Watkins exposure meters 
and as having devised methods of exposure and develop- 
ment whereby the results are rendered more certain than 
by the older “rule of thumb” procedure. In this 
manual Mr. Watkins has systematically set forth his 
methods of timing exposure and development, and as 
these methods are sound in principle and useful in prac- 
tice, acomplete and orderly presentation of them as is 
here given results in a handbook that must be of great 
value to all serious students of the subject. It is the 
most welcome photographic manual that we have received 
for a long time. 
We should have much preferred it if the author had 
remained true to his title and not endeavoured to provide 
a book suitable for two distinct purposes, namely, as an 
exposition of the procedures that he has introduced and 
popularised, and also as a guide for the beginner. Any- 
one who will be instructed by the statements that the 
lens forms the image and that the plate receives the “lens 
image,” that a box of plates must be opened only in the 
dark room, and so on, will be quite unable to appreciate 
the bulk of the volume. Moreover, the author’s 
heart is evidently in those sections of the subject 
that he has made peculiarly his own. In these he is full 
and clear, and probably no one, however much he may 
have studied the matter before, will read these parts with- 
out learning a good deal. The other chapters appear to 
have been written unwillingly, for in them accuracy is 
sacrificed for the sake of an apparent simplicity, and the 
subjects they represent cannot be said to be treated of, 
they are little more than referred to. In learning to 
photograph, as in learning to speak, the natural method 
is first to learn to do what it is desired to do, and finally 
to learn the grammar or the theory. No one tackles a 
subject in the opposite direction except under the com- 
pulsion of a schoolmaster, and then generally he learns 
the subject badly. 
In dealing with chemical and physical changes, one 
must have a mechanical conception of the process, and 
Mr. Watkins is generally happy in his illustrations. But 
when he represents the course of development asa simul- 
taneous reduction to the metallic state of all the particles 
of silver salt made amenable to the action of the de- 
veloper by the exposure, so that as the image gradually 
grows in density these particles are at one stage each 
one-quarter reduced, later one-half, while finally the whole 
of each particle is completely reduced, he selects an illus- 
tration that is not true to fact. Butthis is a mere detail. 
We heartily commend the book to those who know 
how to photograph and wish to increase their knowledge 
and improve their practice. Creal 
Nature Study and Life. By C. F. Hodge. Pp. xv + 
514; illustrated. (Boston, U.S.A.,and London: Ginn 
and Co., 1902.) Price 7s. 
THE author of this little volume is convinced that the 
only true method of nature-study is by making children 
thoroughly acquainted with living animals and their 
ways, both in the wild state and in confinement. He will 
have nothing to do with technicalities as to their structure 
and classification, leaving these, if theyareeverto be taught 
at all, for older pupils. The keeping of tame animals as 
pets, and the history of domesticated animals, so far as 
known, are regarded as important factors in the scheme. 
A similar mode of study is pursued in the case of plants, 
where the pupil is not bothered with a long string of 
technical names or wearied with details as to their 
NO. 1706, VOL. 66] 
structure. Their life and their relations to inanimate sur- 
roundings are the only things it is sought to teach. The 
author’s mode of procedure is to induce the members of 
the class to write down the names of all the animals— 
both wild and domesticated—with which they are 
acquainted, to classify them roughly, and then to discuss 
some of the more important types at length. 
That the authors method is not a mere empirical 
suggestion, which may or may not prove successful in 
the class-room and in the field, is evident from the intro- 
duction to the volume by Prof. Stanley Hall, of Worcester, 
Mass., who writes as follows:—‘‘New as his method 
essentially is, it is now made public only after years of 
careful trial in the public school grades in Worcester, 
until its success and effective working in detail is well 
assured. Thus it has passed the stage of experiment, 
and js so matured and approved that, with slight local 
adjustments, it can be applied almost anywhere for 
children of from six or seven to thirteen or fourteen 
years of age.” 
In the United States the success of the method seems 
indeed to be assured, and there is accordingly every 
inducement to give it a fair trial in this country. The 
book is brightly and pleasantly written and well illus- 
trated. Whether the author is altogether correct in the 
statement on p. 8, that the mammoth was a third taller 
and more than twice the weight of “ our elephant,” and 
that “the mastodon” was larger still, we may be per- 
mitted to doubt. We are also at a loss to know the 
particular kind of fossil deer indicated by the name 
Cervus americanus, a title properly belonging to the 
existing Virginian white-tailed deer. Rew. 
Manual of Agricultural Chemistry. By Herbert Ingle. 
Pp. 412. (London: Scott, Greenwood and Co., 1902.) 
Price 7s. 6d. net. 
AGRICULTURAL chemistry deals with a very extensive 
range of subjects, including the whole of the materials 
and operations with which agriculture is concerned. The 
plant, the soil and the animal are each of them subjects 
sufficient to satisfy a whole generation of workers ; but 
agricultural chemistry includes all these and much more 
besides. No book ever has been written, and none 
probably ever will be, attempting to deal with the entire 
subject ; the student must, therefore, fill his shelves with 
a great variety of books, by many writers, if he would 
have at command the information available on the sub- 
jects of agricultural chemistry. 
The present manual represents the course of instruc- 
tion in agricultural chemistry given at the Yorkshire 
College, Leeds. The course of instruction is a full one, 
and the matter has been carefully written out by the 
lecturer, Mr. H. Ingle. The book thus produced will 
be heartily welcomed by all students of agricultural 
chemistry ; it brings together clearly and correctly a 
great mass of facts which can be found in no other single 
volume. Especial attention is given to questions con- 
nected with pure chemistry, organic and _ inorganic, 
and with physiological and analytical chemistry ; less 
prominence is given to the problems of practical agricul- 
ture. Thus we have the percentage composition of crops, 
but not the composition of average crops per acre ; the 
subject of rotations is also omitted — Again, under animal 
chemistry, we have no discussion of the relation of food 
to animal maintenance, or to the production of work or 
animal increase. The values of foods for the production 
of heat are given, but the extent to which these potential 
values are utilised for animal requirements is not dis- 
cussed. The epoch-making researches of Kellner and 
Zuntz on this subject are not referred to. 
The author describes Grandeau’s method for the de- 
termination of humus in soil, based on the solubility of 
this substance in alkalis. Asa good deal of work is being 
done with this method both in America and in this 
