March 15, 1883} 
NATURE 
457 
hydraulic press, and we are told (vo/e, p. 75) that a cubic 
foot of water possesses, “in virtue of the steadiness of the 
motion, pressure or potential energy,” &c. On p. 74 
“total pressure” is used for resultant pressure. Nowhere 
throughout the book is the theory of the centre of gravity 
given, or the name even defined, yet the author ~— to the 
chagrin of any student who believes it—does not hesitate 
on p. 142 to preface with the words “it is evident”’ an 
application o he usual formulz defining the position of 
the centre of gravity to the case in hand. The term 
“radius of g ration” is used on p. 144, but not defined 
until p. 196. The statement that “velocity is the speed 
with which a body moves’’ reminds one of Lord Palmer- 
ston’s definition of an archdeacon, and we wonder what 
kind of notion will be gained of the motion of a body in a 
curve by any one who is told in a definition of centrifugal 
force that, “if a body is compelled to move in a curved 
path, it exerts a force directed outwards from the centre.” 
We have also the following as a definition of the pitch 
circle :—“ Two spur wheels enter some distance into one 
another, and the circle on one which touches a circle on 
the other, the diameters of these circles being proportional 
to the numbers of teeth on the wheels, is called the pitch 
circle.” Could even the common sense of high quality, pos- 
tulated of the readers of the book, enable them to select, 
from the infinite number of pairs of circles satisfying the 
above conditions, those which represent the pitch circles 
required? 
In the rule for the differential pulley block we are sur- 
prised to find that the movable pulley rises through the 
whole, instead of half, the difference of the amounts of 
rope uncoiled from the two pulleys in the upper block. 
On p. 30 it is said :—‘“‘In the study of the motion of a 
slide valve it is much too usual to assume that the piston’s 
motion is what is shown in Fig. 18 as pure harmonic 
motion.” How shall we reconcile this with the informa- 
tion we have already received on the previous page that 
Fig. 18 (a skeleton drawing of a crank and connecting 
rod) does not represent pure (why not ‘“‘simple?”) har- 
monic motion except when the connecting rod is infinitely 
long? 
In the rule which is inserted on p. 46 to find M, 
the constant should be twice that given, or about 59,500. 
On p. 64 our powers of comprehension are baffled in 
endeavouring to attach a meaning to the assurance that 
“So foot-pounds is the total energy stored up in the wire 
in the shape of a strain.’ (The italics are ours.) In the 
rule given in Art. 192—we presume for evfectly elastic 
bodies—the momentum communicated from the one body 
to the other is just twice that stated. 
We are told (p. 193) that the motion of a point in the 
balance of a watch is very nearly pure harmonic, if we 
suppose the point to move ina straight line instead of a 
circle, but we confess that the advantage of so describing 
the motion is not apparent, nor should we be disposed to 
call the friction in a twisted wire fluid friction (p. 199) 
because the friction in this case, as in that of fluids moving 
slowly, is proportional to the velocity. 
The long array of mistakes given above, which by no 
means exhausts our list, forms a very serious accusation 
against the author. 
His book has much disappointed us, for although 
some of the chapters, such as those on shear and 
twist, beams, graphical statics, and spiral springs, treat 
in a simple manner subjects which in parts present some 
difficulty, yet the defects to which we have alluded are 
far too grave to be compensated by any excellence in 
particular parts of the work. In the earlier chapters 
especially, the author has failed in the fundamental ex- 
cellences of book-writing, in logical arrangement and 
clearness and exactness of expression, in just those quali- 
ties in fact in which he would have been most successful 
if he had aimed at writing more from ‘the standpoint 
of an Alexandrian philosopher.” J. F. Main 
OUR BOOK SHELF 
Der Norske nord-hass-expedition, 1876-1878. VIII. Zoo- 
logi, Mollusca. I. Buccinide, ved Herman Friele. 
Med 6 plancher og 1 kart. 4to. (Christiania ; Gron- 
dahl and Sons, 1882.) 
I HAVE already, in the Annals and Magazine of Natural 
History for this month, given some account of the scientific 
expeditions which were made by the Norwegian Govern- 
ment during the years 1876, 1877, and 1878, to explore the 
sea-bed lying between the coasts of Western and Upper 
Norway and Iceland, Jan Mayen, and Spitzbergen ; and 
I also noticed the series of publications which embody 
the result of these expeditions, including the present 
volume. I now propose to say a few more words on the 
subject of Herr Friele’s work. 
The great family of Buccinum, which is treated in it, 
is most perplexing in a taxonomical point of view; and 
its generic type, Buccinum undatum,is so unusually prolific 
and abundant, and consequently so variable, that no two 
conchologists agree as to the number of species belonging 
to it. In a short paper of mine on the northern species of 
Buccinum, which appeared in the Azma/s for December 
1880, I ventured to consider as varieties of that species and 
of B. grenlandicum (which is probably also a variety of 
the polymorphous ZB. wdatwm) no fewer than 25 other so- 
called species. Such amalgamation will doubtless not be 
admitted by many conchologists ; but the examination and 
careful comparison of an immense number of specimens 
from all parts of the North Atlantic which have fallen 
under my examination, warrant me in forming the above 
opinion. If we were to substitute the German word 
“geste’lt” or form for species, subspecies, and varieties, 
it might perhaps be a more safe and convenient mode of 
definition ; but naturalists are not yet prepared to change 
the time-honoured system of Linnean and Lamarckian 
classification. 
Herr Friele’s work and the other publications fo 
which I have referred are written in excellent English, 
as well as in his native language. The descriptions of 
new species are in Latin, which is scarcely so well 
adapted as English or French for the terminology of 
natural history at the present time ; although his descrip- 
tions are far superior to the barbarous if not illiterate 
productions of Reeve and some other modern concho- 
logists. The distinctive characters of new species are 
for the most part given in the same order, so that the 
description of one species can be more easily compared 
with that of a congener. This is an important and nearly 
indispensable desideratum. One new genus (/uma/a) is 
proposed, having Fusus Turtoni for its type; and it 
appears to be based on Prof. G. O. Sars’s description of 
the odontophore or dentition. Ten species are also for 
the first time described and figured, viz. one of /uma/a, 
seven of Weptunea, and two of Buccinum. I regret that 
I must disagree with my friend the author as to the 
number of genera (six) into which he has divided the 
northern species of Buccinéde. 1 should be disposed to 
attach more value to the operculum than to the odonto- 
phore as a generic character. Nor can I accept all his 
