632 
have been almost equally important revolutions 
in its methods and principles. It is less a col- 
lection of facts and experiments than it once 
was. Indeed, the accumulation of these within 
the past decade has been so rapid, and the col- 
lection is now so vast, as to preclude the idea of 
even an attempt to enumerate them in a text- 
book. Fortunately the accumulation of facts 
has been accompanied by classification and 
orderly arrangement. Theory and _ practice 
have been close companions, each occasionally 
taking the lead. Not many years ago it was 
possible, in a text-book of moderate dimensions, 
to state nearly all of the principal facts relat- 
ing to certain departments of physics, which 
are to-day represented by special treatises, 
numbered by the hundred. ‘The text-book for 
the undergraduate can no longer attempt to 
deal with these matters in detail. It must con- 
fine itself to a consideration of the established 
principles of the science, with such, and only 
such, experimental illustrations as are necessary 
to enable the student to comprehend these prin- 
ciples. Experiments must be typical rather 
than special in form, and of such a character 
that the phenomenon to be exhibited is the 
prominent feature, rather than the particular 
piece of apparatus with which it is shown. 
In the preparation of this book, its author 
has taken a new departure, and largely in the 
direction indicated. In glancing through its 
pages, one is equally surprised, both by the 
presence of many things which he has not be- 
fore seen in text-books of a similar grade, and 
by the absence of many other things to the sight 
of which he has long been accustomed. Of the 
latter, the most noticeable, at first, are the fine 
pictures, the absence of which is a conspicu- 
ous feature of the book: indeed, the charac- 
ter of the work is revealed more promptly 
through this feature than any other. Cuts and 
drawings are introduced whenever, in the opin- 
ion of the author, they are necessary to eluci- 
date the text; but they are generally of the 
simplest character, and such as can readily be 
reproduced upon the blackboard, or added to, 
if thought desirable, by one possessing little 
skill. In describing an experiment, only the 
absolute essentials are shown; the details of 
construction, and special forms of apparatus, 
being left to the imagination of the student, or 
the descriptive powers of the teacher. Per- 
haps the economy exercised in this direction 
has been a little too rigorous; but the plan 
possesses great advantages, both direct and 
indirect. One is spared the elaborate descrip- 
tions of apparatus which occupy so many pages 
of other text-books. It must be admitted that 
SCIENCE. 
able references to eventful periods of discovery 
[Vor. IIL, No. 68. — 
this is, on the whole, a considerable gain. It 
is often difficult to understand a complicated 
instrument from a description and a cut; and 
often the more accurate the latter, the greater 
the difficulty, as much attention will be given 
to the really non-essential parts. Students 
have a perverse way of being interested in the 
architecture of an instrument, and often re- 
ceive a more lasting impression from its ‘ ele- 
vation ’ than from its ‘ground plan.’ It is not 
an uncommon experience to find that a man 
will study an instrument from cut and descrip- 
tion in the text-book, and fail to recognize the 
same thing under a somewhat different form, 
when it is placed on the table before him. It 
would be interesting to know how many under- 
graduate students who have studied electricity 
are able to distinguish the soul of a galvanom- 
eter from its body so completely as to be able 
to recognize it in all of the numerous forms in 
which it materializes. 
Again: in many instances the instrument so 
carefully figured and described in the text-book 
has become obsolete, which can hardly be said 
of the principle involved. . 
The omission of this illustrative and descrip- 
tive part of the text-book is to be commended 
because it leaves room, — it leaves room for the 
introduction of much matter, which is certainly 
more than the equivalent of that which is 
omitted. 
Considerable gain in space accrues from an- 
other noticeable feature of the book, in which 
it differs materially from those more generally 
in use. 
It is not a book of reference. ‘The reader 
will not fail to observe the entire absence of 
tables, and will look in vain for collections of 
physical constants, or of numerical data, or 
of the various and varying results of different 
experiments in quantitative investigations. 
The history and personal aspect of scientific 
discovery will be missed by many, and this 
omission was evidently reluctantly decided 
upon by the author. 
Strip some of our well-known text-books of 
all these, and they will shrink very consider- 
ably in their dimensions. ‘There may be dif- 
ference of opinion concerning the desirableness 
of these omissions. Our author has unques- 
tionably assumed, that, wherever his book is 
used, there will be a good collection of physical 
apparatus, which may be accessible to the stu- — 
dent for examination when desirable; and an 
enthusiastic and competent instructor, who 
knows the history of his subject, and can arouse — 
the interest and enthusiasm of his class by suit- — 
