68 
POPULAR SCIENCE REVIEW. 
As regards the galvanometer , Dr. Radcliffe thinks it of little use in these 
inquiries, compared with the electrometer. The galvanometer does not tell 
us, the other instrument does, that the parts between the poles are charged 
half positively, half negatively. Yet this is intelligence which, the author 
assures us, cannot be dispensed with ; for, as he proves further on, ic the 
workings of voltaic electricity upon muscle are found to be resolvable into 
those of the charge and discharge of these very charges, and not into those 
of the constant current.” 
Another result which the author has arrived at is that the state of the 
muscles is a state of electrotonos , which state further bears out the ideas 
already alluded to. All through the work will be found abundant accounts 
of experiments made by the author and an ample description of the results 
obtained by Matteucci and Du Bois-Reymond, and others who have been 
engaged in similar researches. In point of style, the book is an exception, 
for Dr. Radcliffe writes, as few of his medical compeers can, with an 
elegance and terseness which are most unusual. The physical characters 
of the volume display the publishers’ good taste. 
think, of all the works which Dr. G. Hartwig has given us, the 
present one is unquestionably the best ; not only in its style, which is 
clear and simple, but in the information it conveys, which is full, accurate, 
and modern. We do not see any fault to find with the book, and we are 
sure that our readers will study it with a great deal of satisfaction, and 
with an intense interest in the manifold facts which it relates. The book 
may really be divided into four parts. First, there is the purely geological 
and palaeontological; then comes physical geography; next we have mines 
and mining; and, finally, an account of minerals and gems. All this is well 
done ; and the illustrations, although not excessively numerous, are never- 
theless good ones of their kind. We shall endeavour to quote something 
from the principal sections, and thus give the general reader a better idea 
of the exact nature of the book. After giving a brief account of the different 
fossil forms which we have yet discovered, the author makes the following 
remarks on the important question, Has the animal world diminished in size 
as it has gone on P 
“The colossal size of many of the extinct plants and animals might 
seem to favour the belief that organic life has degenerated from its forme . 
powers ; but a survey of existing creation soon proves the vital prin- 
ciple to be as strong and as flourishing as ever. No fossil tree has yet been 
found to equal the towering height of the huge Sequoias and Wellingtonias 
of California ; and though the horse-tails and club-mosses of the carboni- 
ferous ages may well be called colossal when compared with their diminutive 
representatives of the present day, yet their height by no means exceeded 
that of the tall bamboo of India. No fossil bivalve is as large as the Tri - 
dacna of the tropical seas ; and though our nautilus is a mere pigmy when 
* 11 The Subterranean World.” By Dr. George Hartwig. London : Long- 
mans and Co. 
THE SUBTERRANEAN WORLD.* 
