I885.J 
Analyses of Books. 301 
striking resemblance between the adtion of poisons on the Medusae 
and in the higher animals. 
Fresh water appears to have a deadly influence upon the 
Medusce , — not so rapidly, however, as Professor Agassiz asserts. 
Nor is this influence due, as the same authority holds, to the 
mere difference of specific gravity, since fresh water is still fatal 
to these animals if its specific gravity is raised to that of sea- 
water by the addition of neutral salts or of sugar. 
We must here, however, conclude. The interest of Mr. 
Romanes’ book lies not so much in the advancement of our 
knowledge of the Medusce, considered by themselves, as in the 
light thrown on the origin and development of the nervous system 
in general. As such it is for the naturalist most instructive 
reading, to whom it will not fail to suggest further trains of 
research. 
An Elementary Treatise on Dynamics, containing Applications to 
Thermodynamics, with numerous Examples. By B. William- 
son, M.A., F.R.S., and F. A. Tarleton, LL.D. London : 
Longmans, Green, and Co. 
In this very thorough-going treatise the authors discuss in suc- 
cession velocity, acceleration, the laws of motion, rectilinear and 
parabolic, friction, momentum, aCtion and reaction, impaCt and 
collision, circular motion, including harmonic motion, centrifugal 
force and motion in a vertical circle, work and energy, central 
forces, constrained motion and resisting medium, motion of a 
rigid body parallel to a fixed plane, motion of a rigid body in 
general, small oscillations, dynamical principles and application 
of the theory of energy to thermodynamics. To readers who are 
not mathematicians this work will prove simply unintelligible, 
whilst the student acquainted with the differential calculus will 
find it an excellent, and we think a sufficient, guide in the study 
of dynamics. Although there are examples in abundance we are 
glad not to find a list of questions set, &c., at such and such an 
examination. 
