354 
POPULAE SCIENCE EEVIEW. 
errors and bringing up bis work to tbe present state of scientific knowledge. 
All we can say of tbe editor’s actual labours is, that he has added much new 
matter to the old text, and that he has modified some of Dr. Lardner’s state- 
ments in accordance with currently accepted doctrines and recent investiga- 
tions. The changes by way of substitution and alteration have not been 
extensive, but the additions made have been both numerous and important, 
and may be distinguished from the older letter-press by being included 
within brackets. In Book I. we find, of the editor’s writing, a section on 
the phenomena of the residual charge of the Leyden jar, and a chapter on 
“ Sources of Electricity other than Friction.” The principal additions to the 
department of voltaic electricity relate to Ohm’s law of the intensity of cur- 
rents, the tangent galvanometer, the measurement of conducting powers, the 
rheostat, ozone, the polarization of electrodes, the retardation of telegraphic 
signals by inductive action on submarine cables, and the laws of development 
of heat in the voltaic currents. In this book also we observe that Chapter I., 
and large portions of Chapters III. IY. and XIII., have been completely 
re-written. In the fourth book, which relates chiefly to sound, the changes 
and additions have been less in number, but are not the less valuable. The 
work addresses itself to those who, without a profound knowledge of mathe- 
matics, desire to be familiar with experimental physics, and to such we 
especially recommend it. The medical student will find in its pages almost 
everything that is essential to a thorough knowledge of electricity and 
acoustics. 
