472 
NATURE 
j]cry 11; row 
of this kind at some former stage in the earth’s 
history. It is impossible here to summarise the 
discussion, which is somewhat intricate, but Prof. 
Love’s verdict—and there can be no_ better 
authority—is, on the whole, unfavourable to the 
suggestion. 
The concluding sections of the book deal with 
the propagation of seismic waves. This is at 
the present time a question of the highest interest. 
Instruments have been greatly improved, and the 
records make an increasing claim to be regarded 
as faithful transcripts of the earth-movements. 
Phases more or less conspicuous are recognised 
in the diagrams, and are successfully used for the 
location of distant centres of disturbance. But 
the details of the records, and in particular the 
predominance, at different stages, of oscillations 
of various periods, offer much that is perplexing. 
For instance, it is difficult to account for the resolu- 
tion of a transient shock, as it proceeds, into a 
series of oscillations of gradually changing period 
except on the hypothesis of something analogous 
to “dispersion” in optics, the essence of which 
is a variation of wave-velocity with wave- 
length. General elastic theory, on the other 
hand, suggests constant wave-velocities, whether 
in the case of the longitudinal and_ trans- 
verse vibrations, which are supposed to be pro- 
pagated through the body of the earth, and to con- 
stitute the first and second phases of an earth- 
quake disturbance, or in that of the larger ‘“ Ray- 
leigh” waves, which travel over the surface. 
This theory, however, takes no account of gravity, 
or of variation of density and elastic properties 
with depth. Prof. Love has no difficulty in show- 
ing that when such circumstances are taken into 
consideration some amount of “dispersion” 
ensue. : 
must 
There is another particular in which the general 
theory appears to be inadequate. When the 
larger waves set in at any place, the horizontal dis- 
placement of the ground may at first be partly or 
even mainly transverse to the direction of propa- 
gation, whereas in the “Rayleigh” type of waves 
the horizontal component is longitudinal. Prof. 
Love meets this difficulty by the hypothesis that 
the earth consists of a comparatively thin crust, 
resting on a core which is denser and of different 
elastic properties. In this way it is possible to 
reconcile the fact of transverse displacement with 
(practically) superficial propagation; moreover, 
dispersion, almost as a matter of course, makes 
its appearance. We believe that this theory is 
worthy of careful examination; but much remains 
to be done in the way of quantitative as well as 
qualitative comparison with actual seismograms, 
before any decisive verdict can be passed upon it. 
NO. 2228, vot. 89] 
It will be seen from the above rapid outline that 
the work under review deals with problems of 
great difficulty, but of the utmost interest, in a 
rapidly developing branch of science. It is need- 
less to say that they are treated with great mathe- 
matical skill. The book received, indeed, the 
Adams for the year to11. This prize 
is remarkable, even among similar foundations, 
for the high quality of the work which it has called 
forth. Many of the treatises thus produced, e.g., 
Maxwell’s essay on Saturn’s rings and Routh’s 
on stability of motion, not to mention others by 
living authors, have become classics. It is no slight 
praise to say that Prof. Love’s work is worthy of 
the distinguished company in which it finds itself. 
jails be 
Prize 
ELECTRICAL ENGINEERING. 
The of Electrical Transmission. A 
Text-book for Colleges and Technical Schools. 
By Prof. O. J. Ferguson. Pp. vii+457- (New 
York : The Macmillan Company ; London: Mac- 
millan and Co., Ltd., 1911.) Price 15s. net. 
Direct and Alternating Current Manual. With 
Directions for Testing, and a Discussion of the 
Theory of Electrical Apparatus. By Prof. F. 
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Second Edition, enlarged and revised. Pp. 
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Storage Batteries. The Chemistry and Physics of 
the Lead Accumulator. By Protaaeaave 
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Maschinen und Apparate der Starkstromtechnik : 
ihre Wirkungsweise und Konstruktion. Erster 
Teil: “Gleichstrom.” Zweiter Teil : “ Wechsel- 
strom.” By Gustav W. Meyer. Pp. xiv +590. 
(Leipzig and Berlin: B. G. Teubner, 1912.) 
Price 15 marks. 
ss LECTRICAL Transmission” covers a 
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Elements 
movers, switch-boards, 
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instruments, and other matters pertaining to the 
use and sale of electricity after it has been trans- 
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practical, although, as may be expected, American 
practice predominates. This is no drawback, 
since for high voltage long-distance transmission 
English readers cannot do better than study the 
details of the work done in America, but there 
synchronous 
