
NATURE 
[APRIL 22, 1915 

OUR BOOKSHELF. 
Manual of Oils, Resins, and Paints, for 
Students and Practical Men. By Dr. H. Ingle. 
Vol. I., Analysis and Valuation, by the author 
and J. A. L. Sutcliffe. Pp. 129. (London: C. 
Griffin and Co., Ltd., 1915.) 3s. 6d. net. 
Tus small volume is intended for students, 
analysts, and works chemists who are familiar 
with general chemistry but have had little or no 
practical experience in analysing oils, or prepara- 
tions which contain oils. It includes much of 
what one would put in a good notebook intended 
for personal use in the laboratory. A short intro- 
duction serves to refresh the reader’s memory 
upon points in organic chemistry specially rele- 
vant to oils and fats, after which the authors give 
short accounts of the most approved chemical and 
physical methods used in examining these bodies. 
Theoretical explanations are included as well as 
practical details. For example, the chemical re- 
actions concerned in the absorption of iodine by 
oils are described more fully than usual—though 
it is true that we have to look in more than one 
place for them. A chapter on_ technological 
analysis deals not only with oils, fats, and waxes 
as such, but with articles such as paints, pig- 
ments, and varnishes which may contain oil as an 
ingredient, and with allied substances, such as 
turpentine and gum-resins. 
The correct interpretation of the results ob- 
tained would often require much more knowledge 
than could be obtained from the descriptions 
given. Information as to the origin and methods 
of preparation of the various oils is not within 
the scope of the work. It is understood, how- 
ever, that further volumes are to follow, dealing 
with these matters. The book is a useful intro- 
duction to laboratory work in the subject. 
ny 
Potting, for Artists, Craftsmen, and Teachers. 
By G. J. Cox. Pp. ix+200. (New York: The 
Macmillan Co.; London: Macmillan and Co., 
Ltd., 1914.) Price 5s. 6d. net. 
Tue book will prove a distinct help to an artist 
craftsman who wishes to “do something” with 
clay. The author is right in saying: “Too much 
stress cannot be laid upon the importance of | should refer to Tait’s ‘Properties of Matter,’’ for I 
close study of the best work, both ancient and 
modern, for it is a truism that however handily 
a craftsman may work, his output will be worth- 
less if he has not, with his increasing powers of 
technique, developed a sound judgment and re- 
fined taste.” The description of the various 
simple processes of pottery work is very exact, 
and the illustrations are admirable. 
The book, indeed, is a simple, though thorough 
and concise, first tutor to an artist craftsman, 
and should, to use the author’s words, ‘‘set one 
or two sincere students to the making of some 
of the many beautiful objects of utility and art 
with which the craft abounds.” 
The list of pottery terms is useful, though there 
are a few which are not employed in this country 
in the sense given by the author, for example, 
NO. 2373, VOL. 95] 

clammings in England means the doors of the’ 
kiln, and not simply the sand or siftings applied 
to the cracks in them; pug in this country is 
used to mean the mechanical wedging of clay; 
galena is classed by the author as highly poison-. 
ous, and lead as poisonous, whereas galena is 
practically safe to use, but there may be con-. 
siderable danger ‘in using white lead carelessly. 
BERNARD Moore. 

BEDTERS TO) TE SED TiO 
[The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Narure. No notice is 
taken of anonymous communications. | 
The Princinle of Similitude. 
Wuen Lord Rayleigh directs attention to the 
neglect among physicists of the principle of similitude 
(NaturE, March 18), he has perhaps forgotten the 
| excellent paragraph in which Tait deals with the 
question in his ‘‘ Properties of Matter.’’ Curiously 
enough, one of Lord Rayleigh’s first illustrations is — 
also Tait’s, namely, the fact that the velocity of waves. 
on deep water is as the square root of their lengths, 
to which Tait adds the corresponding fact that the 
| velocity of ripples is inversely in the same proportion. 
The principle is of great use in biology, as Herbert 
Spencer was the first to show. By its help we under— 
stand how there is a limit set to the possible growth 
in magnitude of terrestrial animals; how, on the 
| other hand, the whale gains in activity and speed the, 
bigger it grows; why the ostrich is unable to fly; 
why the bee’s wing vibrates so much quicker than a 
| bird’s; and why the flea can jump well-nigh as high 
| paragraph in question. 

as a man. And not less does the principle deserve to- 
be borne in mind when we consider what must be 
the conditions of life in the most minute organisms : 
especially if there be any so small as that Micrococcus 
of the rabbit, the diameter of which is given in the 
books as only o-oco015 mm., or not far from the limits. 
of microscopic vision. 
D’Arcy W. THOMPSON. 
Ir is rather curious that Prof. D’Arcy Thompson 
fancy I might claim some part of the credit for the 
In a review of the first 
edition (Nature, vol. xxxii., p. 314, 1885) I wrote :-— 
“There is one matter suitable to an elementary worl: 
which I should be glad to see included in a future 
edition, viz., the principle of dynamical similarity, or 
the influence of scale upon dynamical and physical 
phenomena. It often happens that simple reasoning 
founded upon this principle tells us nearly all that is 
to be learned from even a successful mathematical 
investigation, and in the numerous cases where such 
an investigation is beyond our powers, the principle 
gives us information of the utmost importance.” 
And, after an example or two: ‘“‘I feel sure that in 
Prof. Tait’s hands this very important and funda- 
mental principle might be made intelligible to the 
great mass of physical students.’ Though I believe 
I was in correspondence with him at the time, I do not 
| remember to have seen Tait’s second (or later) edition, 
