[February, 
96 
Analyses of Books . 
Experimental Researches into the Properties and Motions of 
Fluids , with Theoretical Deductions therefrom. By W. 
Ford Stanley. London : E. and F. N. Spon. 
We have here before us the results of a prolonged and laborious 
inquiry into the theoretical conditions of the fluid state and the 
motive properties of forces in fluids. The author, some years 
ago, appears to have undertaken an experimental examination of 
the undulatory theory of light, and, as this theory is generally 
illustrated by simili.udes taken from water-waves and sound- 
waves, he was led to examine these latter motions to be assured 
that the illustration is not misleading. He accordingly set about 
observing the motive effedls evident in the directions taken by 
impressed forces in fluids under various principles of resistance. 
He came to the very legitimate conclusion that much work re- 
mains to be done before the principles of hydro-dynamics can be 
fixed with the needful precision. Some of this work he has 
attempted to do, and the results are presented in the present 
volume. 
The first three chapters Mr. Stanley admits to be “ speculative, 
and even in parts hypothetical.” 
In the second chapter, dealing with the conditions of liquid 
surfaces, he rejedts the theory of tensile surfaces for liquids as 
recognised, e.g., by Clerk Maxwell, and takes the opposite view, 
that such surfaces are extensile instead of tensile , “ except for 
free films which are clearly tensile by the position of the attractive 
matter which composes them.” These terms “ tensile ” and 
“ extensile ” he defines as follows : — By tensile I intend a dis- 
position of the parts of a system of matter to draw themselves 
together as a stretched drum-skin does. By extensile I intend 
the reverse of this, or the disposition of the parts of a system 
of matter to separate, and thereby to engender external pressures.” 
He considers that his view is supported by the familiar experi- 
ment of floating a needle upon the surface of a vessel of water. 
He pronounces the subject, however, insufficiently worked out. 
Some of the propositions in the third chapter will also, it is 
said, need partial correction. We notice especially the author’s 
106th proposition, which runs that “ a projectile or a flowing 
force forming the head of a current before the continuity of pro- 
jection can rotate a large volume of the resistant fluid laterally, 
will divide its direct current by constant bifurcation until the 
projectile force becomes in equilibrium with the forward resist- 
ance.” This proposition he proves, or at least illustrates, by the 
following experiment: — “ Take a pen full of ink, and place this 
gently upon the surface of the water in the trough a glass 
trough, narrow in proportion to its height). The ink, as it 
descends slowly by gravitation, will be found to divide constantly 
