126 Reviews—H. Jeffreys—Interior of the Earth. 
thrown on the question of the age and origin of the tin-bearing clays 
of the Kinta district, concerning which Mr. Scrivenor’s former 
assistant, Mr. W. R. Jones, is in disagreement with him. 
There is a brief account of gold workings under native management. 
The statement that certain men ‘‘obtained in a season 2-3 katis of 
gold per party of three men. This is equal to 24-36 bungkals of 
gold”’ does not convey much information to the average reader of the 
report at home. Such words as prkul and ulu might also with 
advantage be explained in a footnote. 
IJ.—Txe Inrerior or THE Harta. 
Certain Hyporueses as To THE InTERNAL SrRucTURE oF THE Kant 
anD Moon. By Harrorp Jerrreys, B.A., M.Sc. Mem. Roy. Ast. 
Soc., lx, pt. v, pp. 187-217, 1915. 
Tue Viscosrry or THE Earta. By H. Jerrreys. Monthly Notices 
Roy. Ast. Soc., xxv, pp. 648-58; Ixxvi, pp. 84-6, 1915. 
Tue MecwanrcaL Propertizs or THE Karta. By H. Jerrreys. The 
Observatory, No. 491, pp. 347-51, 1915. 
laa gradual refinement of geophysical methods of research 
during recent years has resulted in the accumulation of quite 
a considerable fund of information relating to the interior of the 
earth. The known data from which our present knowledge is derived 
are—(1) the value of the precessional constant, (2) the earth’s 
superficial ellipticity, (8) the period of the variation of latitude, 
(4) the observed heights of oceanic tides, (5) the lunar deflection 
of gravity, and (6) the velocities of earthquake waves. Using the 
results available from these sources, Mr. Jeffreys discusses those 
hypotheses that regard the earth as consisting primarily of a metallic 
core surrounded by a rocky sheli, particularly from the point of 
view of determining the distribution of rigidity and density. 
He shows that neither the outer shell nor the inner core can be 
permanently rigid, and that the only conclusion consistent with the 
facts is that the earth as a whole is plastic. Again, the only 
distribution of density conformable with this conclusion is that of 
Wiechert, viz. a shell of density 3:2 surrounding a core of density 
8-2 having a radius equal to 0°78 that of the surface. These 
figures are, of course, closely in accordance with the densities of stony 
and iron meteorites, and with the facts deduced from the seismic 
exploration of the earth’s interior. That the rigidity of the core is at 
least twice that of steel is a necessary consequence of the effect of 
pressure, if the main constituent of the core is metallic iron. 
Mr. Jeffreys shows that the lithosphere has the hydrostatic form to 
a high degree of accuracy. This fact, combined with the deduction 
that the earth’s rotation was originally faster than now, leads us to 
conclude that the outer shell (at least) must have periodically adjusted 
itself to the hydrostatic form. Chamberlin has rejected this view, 
partly because it seems to imply that mountain ranges—particularly 
the older ones—should be meridional in their alignment. However, 
it seems to the present writer that the greatest adjustment may — 
have occurred in a period antecedent to any now recognized. Such 
