JULY 22, 1915] 
NATURE 
aay 

The Nanking professor’s pioneer afforestation 
work, based on co-operation with the Chinese 
gentry, deserved description. Some details were 
published in the National Review (China) of 
April 25, 1914, the list of species employed being 
given, etc. The great difficulty of afforestation 
in China seems to be danger from fire, 200,000 
trees, for example, having been burnt in the ex- 
perimental plantation on Purple Mountain in 1913. 
Professor Baillie since then has established fire- 
lines, 30 to roo ft. wide, which are let to Chinese 
farmers, who keep these lines cultivated and at 
the same time take care of the adjoining planta- 
tions. 
The book is illustrated by thirty-three repro- 
ductions of photographs, some of which have 
appeared in well-known books of travel. Those 
taken from Major Osaki’s ‘““O Ryoko” represent 
well the methods of logging and rafting timber 
in Manchuria. Twelve photographs by Mr. 
Purdom, a recent plant collector in North China, 
are of unequal merit, that of the Chinese horse- 
chestnut being the best. There is also a good 
picture of Pinus bungeana at Peking, a tree often 
planted in temple grounds, the bark of which is 
of a milky-white colour, and peels off in patches 
like a plane, thus giving the stem an extraordinary 
appearance. 

DYNAMOMETERS. 
Dynamometers. By Rev. F. J. Jervis-Smith. 
Edited and Amplified by Prof. C. V. Boys. 
Pp. xvi+267. (London: Constable and Co., 
Ltd eions)) Price 14s: met. 
HE late Mr. Jervis-Smith, a vicar at Taunton 
until in 1886 he took charge of the Millard 
engineering laboratory at Oxford, was a very 
modest and ingenious enthusiast in the experi- 
mental study of natural science. He was 
particularly absorbed in the study of methods of 
measuring mechanical power. A dynamometer 
measures the product of force into velocity. The 
chemical balance illustrates the great accuracy 
with which we can measure force and there is also 
great accuracy possible in measuring speed, but the 
measurement of their product with accuracy is a 
very different thing. To measure the electrical 
power given out by or given to a machine is very 
easy; however large or small the power may be, 
our measurements may be made accurate to the 
fourth or even to the fifth significant figure. It is 
only in very exceptional cases that the measure- 
ment of mechanical power is correct to two 
significant figures. 
Mr. Jervis-Smith left his MSS. in an incomplete 
NO. 2386, VOL. 95] 

form. The book is not a mere collection of lecture - 
notes; many parts of it are quite finished, but on 
the whole it is rather disconnected. The author’s 
sympathetic and admiring friend, Prof. C. V. Boys, 
has edited the book, and he has done this evidently 
as a labour of love. He has not attempted to 
make the book a complete treatise, but he has 
introduced between brackets interesting  state- 
ments and amplifications which tend to make it 
a connected whole. 
The author does not confine himself to dynamo- 
meters. He gives accounts of integrators, plani- 
meters, and other contrivances which are related 
in one way or another to his main subject. We 
get the idea that this is a scrapbook in which 
he placed anything that interested him. There are 
places—as at the beginning, but elsewhere also— 
where he is evidently writing a book, but in other 
places we have evidence of scissors and paste. It 
seems to have been his intention not just to print 
these scraps, but to use them as a foundation for 
better descriptions of his own. We are glad to 
have them, as they would otherwise have to be 
searched for in many publications, and although 
some of them might have been omitted with 
advantage, we regret that they are not more 
numerous. 
There are parts, as when he deals with friction 
and planimeters, where he gives a valuable, 
exhaustive list of references. If he had lived he 
would no doubt have done the same for other 
parts of the subject. Sometimes, as in the rope 
dynamometer brake (p. 71), the descriptions are 
not easily understood as no figure is shown, and 
indeed all the rope dynamometer part is rather 
weak. The descriptions of the water brake of 
Froude and other things are too long and yet 
simple explanations are wanting. A certain air 
brake is described in too much detail, and the 
account of the behaviour of a copper disc moving 
in a magnetic field is tedious. The account of Borda 
“On the Flow of Fluid from Orifices in Vessels” is 
quite out of place in this book. A short account 
of General Morin’s work on friction wouid be 
better than a translation of the original paper. 
We feel sure that if the author had lived he would 
have made the whole book as perfect as part of it 
is, but we can understand why the editor may 
have been unwilling to discard or alter too readily 
some of the things we have mentioned. After all 
they are interesting. The book gives the most 
interesting and complete account of dynamometry 
that is known to us, and it owes a great deal of 
its interest to the additions made by the editor. 
In a few places we think that Prof. Boys is not 
quite fair. Mr. S. G. Brown did not merely 
