344 
NATURE 
[June 6, fror2 
create a vague impression. For example, in 
dealing with the question of acceleration, we find 
stated :——“Let a body move in a straight line, 
and measure its velocity. At one instant it is 
200 cm. per second; 10 seconds later it is 350 cm. 
per second.” Yet there is no indication of the 
mode of measurement, nor is an instantaneous 
velocity even defined. Further, a considerable 
amount of space is wasted in rather absurd dia- 
grams of common objects to which the principles | 
of physics apply, and in portrait drawings of | 
various famous physicists, both of which features 
the authors regard as likely to stimulate the 
interest of students. Speaking generally, it may 
be said that this book contains too much detail for 
a popular exposition, and too little exact informa- 
tion for truly scientific study. 
(5) Several curious features are to be found in 
the laboratory manual also. It is intended to 
accompany the theoretical treatment in the 
previous book, to which reference is always made 
in connection with the experiments. One cannot 
help thinking that some of the observations are 
purely imaginary, and not actually carried out by 
the students. Experiment 36, for instance, is on 
the measurement of the velocity of sound in air 
with a stop-watch and a gun. 
required at about a mile apart. 
gun and the other a stop-watch. The usual pro- 
cedure follows. If a breeze is blowing, the 
observers should change positions, and so on. An 
alternative, and equally absurd, method is also 
described. Most of the experimental work is 
quite simple, but the instructions are not always 
clear, and considerable individual help on the part 
of the teacher would be indispensable to the 
students. The printing, both in this book and the 
accompanying one, is very good. 
(6) Prof. Ebert’s book is a large volume com- 
prising the theoretical treatment of mechanics and 
heat. In using the word ‘ mechanics,” however, 
it must be understood that the first section of the 
book is concerned with sound, and what is usually 
styled “properties of matter,” even more than 
with mechanics in the sense of applied mathe- 
matics. Indeed, the somewhat disordered mix- 
ture of these subjects is the only serious objec- 
tion to the book. It is difficult to understand, 
for instance, why the definitions of the absolute 
units of force and work are postponed to so late 
a stage (p. 216), especially in view of the fact 
that such subjects as elasticity and osmotic pres- 
sure have been considered previously. 
The second part of the book is distinctly 
superior to the first. A more logical treatment 
renders it more easy to follow, the subject is con- 
sidered in greater detail, and none of the important 
NO. 22 3, VOL. 89] 
Two boys are | 
The one has a | 
principles of thermo-dynamics nor their applica- 
tions are omitted. Taken on the whole, the book is a 
good one, and has evidently been prepared with 
great care. One of the chief features is the large 
number of experiments which are described—in 
fact, the book is essentially an experimental 
treatise. These experiments are illustrated with 
carefully prepared diagrams, and numerous 
numerical examples form a useful addition to the 
text. 
(7) This is yet another practical physics 
manual, compiled in this case for the students in 
Calcutta University and in use there for the inter- 
mediate course. It consists of instructions for 
the performance of a few simple experiments in 
each of the branches of physics, together with 
some information regarding general laboratory 
processes such as glass-blowing. There is little 
to distinguish the book from many of a similar 
kind. Fewer experiments, perhaps, are under- 
taken, one only—the resonance tube—constituting 
the whole section on sound. The instructions are 
clearly stated, but the printing and the diagrams 
leave much to be desired. The latter failing is, 
however, common to many books produced in 
India. 
THE TESTING OF BUILDING STONES. 
Handbuch der bautechnischen Gesteinspriifung. 
By Prof. J. Hirschwald. Erster Band. Pp. xi 
+387. (Berlin: Gebriider Borntraeger, 1911.) 
Price 20 marks. 
N this country, and to a great extent else- 
where, the testing of building stones has 
fallen short of the precision attained in the testing 
of other materials of construction. This has been 
due partly to the lack of any generally recognised 
standard methods, and partly to the neglect of the 
petrological characters peculiar to stones of 
different kinds. 
Tests of building stones are usually ‘made for 
two distinct purposes, namely, to measure their 
| comparative resistance to mechanical stresses and 
to find their relative capacity of resistance to 
weathering. 
It certain quarters it has been the practice to 
decry the testing of building stones on the ground 
that it is unnecessary, since any stone worth 
employing at all will be strong enough for the 
purpose; and as to weathering, since that may be 
regarded as “an act of God,” it is no use troubling 
about it. Some, while admitting that tests may 
be desirable, have no faith in the methods usually 
employed, and suggest rather an examination of 
the rocks in the field and in the quarries. There 
is something to be said for this point of view, 
