i88i.] 
Analyses of Books. 
555 
formula. The best means of rapid approximation to mean sec- 
tional velocity he considers to be the measurement of central 
mean velocity. The reduction, however, must be accomplished 
by means of special experiment at each locality. 
Among the minor results must rank the observation that “ the 
motion of water in large open channels is essentially unsteady ; 
even in long, straight, and fairly uniform reaches the velocity at 
any given point is extremely variable from instant to instant, and 
the stream lines interlace freely in all directions.” The maximum 
velocity past any vertical is, as a rule, below the surface. To 
measure mean velocity past a vertical the immersed length of 
such rods must be decidedly less than the depth of the water. 
That this work is a valuable contribution to hydraulic science, 
and that it will repay engineers for a careful study, is our decided 
opinion. 
The Phenomena of the Electric Discharge with 14,400 Chloride 
of Silver Cells. A Discourse by Dr. W. De la Rue, F.R.S., 
delivered before the Royal Institution. 
The battery used in the author’s experiments, but a solid electro- 
lyte, silver chloride, is substituted for the sulphate of copper 
solution. It is impossible to give an abstract of the subjeCt 
matter without the very numerous illustrations contained in the 
pamphlet. 
Solutions of the Questions in Magnetism and Electricity set at 
the Preliminary Scientific First B.Sc. Examinations of the 
University of London from i860 to 1879. Together with 
Definitions, Dimensions of Units, Miscellaneous Examples, 
&c. By F. W. Levander, F.R.A.S. London : H. K. 
Lewis. 
Whatever the excellence of this work in other respeCts, we 
cannot do other than characterise it as the outcome of a radically 
vicious system, — that, namely, which makes it the student’s great 
task not to acquire a thorough mastery of his subjeCt with a view 
to becoming himself a successful interrogator of Nature, but to 
prepare for passing examinations. We cannot blame Mr. Le- 
vander, connected as he is with University College, and conse- 
quently with so purely an examinational body as the University 
of London, for adapting himself to existing circumstances ; but 
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