410 Scientific Intelligence. 
Roy. Soc., No. 136, 1872). (Abstract). 7 yao author passes in eo 
review the principal theories which in modern times have 
proposed to account for voleanic activity, 
The chemical theory, which owed its partial acceptance chiefly 
to the fame of Davy, may be dismissed, as all known facts tend 
to show that the chemical ene rgies of the materials of our globe 
were almost wholly exhausted prior to the consolidation of its 
2 se 
s 
The mechancial theory, which finds in a nucleus still in a state 
of liquid nen a store of heat and of lava, ete., is only tenable 
on the admission of a very thin solid crust ; and even caeomgl a 
crust of about 30 miles thick it is difficult to see how surface-water 
is to gain access to ” fused nucleus, yet without water there can 
be no volcano. More recent investigation on the part of mathe-. 
maticians has been su panel to prove that the earth’s crust is not 
thin. Attaching little value to the calculations as to this, based 
on precession, the author yet concludes, on other grounds, that the 
solid crust is probably of great thickness, and that, although there 
is evidence of a nucleus much hotter than the crust, there is 
certainty that any part of it remains liquid; but if so, it is in any 
case too deep to render it conceivable that poe wb should 
make its way down to it. The results of geological spent 
and of physico- snathemationl reasoning thus oppose each other, 8° 
that some source of volcanic heat closer to the erage venana 
be sought. The h hesis to supply this, pro Hopkins 
and adopted by Piel viz: of i ooeaea pay bts taleos of liquid 
matter infusion at no great depth from the surface remaining fuse 
unded b 
for ages, surroun y colder and solid rock, and with (by hyp 
thesis) access of surface-water, the author views as feeble a ub- 
sustainable. bie 
source, then, for voleanic heat remains still to be found ; 
if found under conditions admitting to it water, opel? of cra 
sea, all known phenomena of volcanic action on our earth’s 
face are explicable. 
author points out various relations and points of connec 
tion pecirece voleanic phenomena, seismic phenomena, and the 
lines of mountain elevation, which sufficiently indicate ‘hat they 
are all due to the play of one set of cosmical forces, thoug 
ferent in degree of energy, which has been constantly decaying 
with time. 
He traces the ways in which the contraction of our globe a 
been met, from the period of its original fluidity to the prese” 
state: first, by deformation of the spheroid, he oi generall 
e oar, of mountain elevation ine 
C. Prevost was the oaly 1 true one—that which asc ribes 
ang d solid crust of sufficient 
uced by the 
ressures pone prod 
