Wi ae 
634 
Under the general head of ‘ ether-waves,’ the 
unity of the so-called heat, light, and actinic 
rays is explained. The theory of exchanges, 
and Stokes’s law, are considered. 
ment of color is extremely satisfactory. The 
origin and propagation of ether-waves, reflec- 
tion, refraction, and polarization, together 
with the postulates of Fresnel, Neumann, and 
MacCullagh, occupy considerable space. All 
of this precedes what is generally known as 
geometrical optics, which is not elaborately 
discussed. In double refraction the Huyghe- 
nian construction is given, and the study 
of optical instruments is remarkable for its 
brevity. 
Electricity and magnetism are provisionally 
defined as properties or conditions of matter, 
the matter referred to being that extraordinary 
form known as the ether. Just enough in the 
way of experiment is given to enable the 
student to understand the development of 
the principles of the subject, which are estab- 
lished under the assumption that he has 
mastered the chapter on attraction, potential, 
etc., already referred to. Some of the notable 
features of this part of the work are more than 
ordinarily intelligible discussions of thermo- 
electricity, Peltier’s and Thomson’s ‘ effects,’ 
the presentation of Maxwell’s theory, with his 
electromagnetic theory of light, and brief 
mention of Rowland’s, Kerr’s, and Hall’s ex- 
periments. There is also a comparison of 
units in the electrostatic and electromagnetic 
systems, and a discussion of the meaning and 
value of the constant v. The arrangement 
of topics in electricity and magnetism may 
be criticised, in that it would seem desirable 
to have introduced the subject of magnetism 
and magnetic potential at an earlier stage, 
thus making possible an earlier exposition 
of the origin of the electromagnetic units of 
measure. 
In connection with the matter of units, it is 
worth while to remark, that throughout the 
work the author has felt constrained, possibly 
out of respect for an unwholesome English 
prejudice, to make frequent use of the foot, 
inch, pound, ounce, grain, etc. Itis, perhaps, 
hardly fair to expect an English author to 
adhere strictly to the use of the metric system ; 
but in the present instance the confusion of 
the units is a blemish all the more noticeable 
by reason of the otherwise simple and elegant 
methods of treatment. Clumsiness of state- 
ment and solution is frequently the unavoid- 
able result. No evidence of this is needed ; 
but it may not be amiss to quote from so con- 
servative a source as Thomson and Tait (Nat. 
SCIENCE. 
The treat- — 
phil., art. 408), who, although selecting the 
.foot as being ‘for British measurement gen- 
erally the most convenient,’ remark, that ‘* the 
British measurements of area and volume are 
infinitely inconvenient, and wasteful of brain- 
energy and of plodding labor. ‘Their contrast 
with the simple, uniform metrical system of 
France, Germany, and Italy, is but little 
creditable to English intelligence.’’ 
Not the least remarkable feature of the book 
is, that its author is a lecturer in a medical 
school, and it ‘‘ was primarily designed as a 
contribution to medical education.’’ : 
Altogether the book must be regarded as 
one oreatly in advance of those of a similar 
grade generally in use. It is not intended as 
a substitute for a laboratory and laboratory 
practice, for no book can be this; but it is 
admirably adapted for a preparation to a 
laboratory course, in that it furnishes the 
student with such ‘‘a store of general prin- 
ciples, that, when he comes to enter a physical 
laboratory, he may then find around him, in 
the concrete form, a collection of pieces of 
apparatus the construction and the action of 
which he is able, by the application of prin- 
ciples already familiar to him, pros and | 
intelligently to comprehend.’’ 
The belief ‘that such a text-book will be 
gladly welcomed by many teachers of physics 
in this country may justify the somewhat ex- 
tended reference to its character and contents, 
given above. 
PROPAGATION OF TUBERCULGE 
The influence of heredity and contagion on the prop- 
agation of tuberculosis, and the prevention of inju- 
rious effects from consumption of the flesh and 
milk of tuberculous animals. By A. LypTIn, 
Carlsruhe, veterinary adviser to the Baden goy- 
ernment; G. Fiemine, LL.D., F.R.C.V.S., 
principal veterinary surgeon to the British army; 
and VAN HERTSEN, veterinary surgeon, and 
chief inspector of the Brussels abattoir. New 
York, Jenkins, [1684]. t/a p. ye 
Turs volume is a translation, by one of the 
committee upon its preparation, of a report 
prepared for discussion at the International 
veterinary congress, held at Brussels in Sep- 
tember, 1883. The question of the etiology 
of tuberculosis is one of the most important 
of modern medicine, and occupies the atten- | 
tion of a large part of the profession to-day. 
Its importance is not confined to the human ~ 
race, in so far as it attacks mankind; but, be- — 
