I 882 .J 
30i 
Analyses of Books . 
draining a continent which stretched far into the Atlantic ; the 
strata formed in its estuary now extends from the Vale of 
Wardour, in Wiltshire, to the Boulonnais in France, a distance 
of 200 miles.” Surely whatever evidence exists for the former 
existence of such a river ought to be taken into account in dis- 
cussing the difficult question of the permanence or mutability of 
land and sea areas. The opinion is now widely entertained 
that former extensions of land have existed where the seas are 
now shallow, but that the beds of the great oceans are, and have 
been, permanent depressions in the earth’s crust. As the ques- 
tion to us at least seems not fully decided, we think the con- 
siderations to which Mr. Harrison refers ought to be carefully 
weighed. 
In ending this brief notice we must express our conviction 
that the “ Geology of the English Counties” supplies and fills 
up an important gap in the literature of the science, and will 
be found a most valuable book of reference. 
Vibratory Motion in Sound. By J. D. Everett, M.A., D.C.L., 
F.R.S., F.R.S.E., Professor of Natural Philosophy in the 
Queen’s College, Belfast. London : Longmans and Co. 
The branch of physics which treats of sound has latterly risen 
in importance, and may now fairly claim an equal rank with 
optics, thermology, and the sciences of electricity and mag- 
netism. In the work before us we have a mathematical treat- 
ment of the subject of vibratory motion. In the successive 
chapters the author treats of simple harmonic vibration ; of the 
composition of motions of translation ; the composition of vibra- 
tions of the same period ; of simple harmonic undulation ; of 
the composition of two simple undulations of the same wave- 
lengths, or of different periods ; the propagation and reflection 
of sonorous undulations ; on the stationary vibration of strings 
and columns of air ; on the energy of vibrations ; on simple and 
compound tones, and on musical intervals. 
The treatise is specially intended for students already versed 
in the elements of dynamics. 
