[ 59 § ] 
of all kinds of earth, ftones, &c. but as the com* 
preffion of the materials immediately over the cavity, 
would 
Jive force is immenfely great. The comprelfibility and elafticity 
of the earth may be collected, in fome meafure, from the vibration 
of the walls of houfes, occafioned by the paffing of carriages in the 
dreets next to them. Another inftance to the fame purpofe, may 
oe taken from the vibrations of fteeples, occafioned by the ringing 
of bells, or by gufts of wind: not only fpires are moved very con- 
fiderably by this means, but even ftrong towers will, fometimcs, be 
made to vibrate feveral inches, without any disjointing of the mor- 
tar, or rubbing of the Hones againft one another. Now, it is ma- 
mfeft, that this could not happen, without a confiderable degree of 
comprelfibility and elafticity in the materials, of which they aro 
compofed : and if fuch frnall things as the weight of fceeples, and 
the motion of bells in them, or a guft of wind, are capable of pro- 
ducing fuch effe&s, what may we not expe& from the weight of 
great depths of earth ? There are fome circumftances, whichYeem 
to make it not altogether improbable, that the form and internal 
ftrudiure of the earth depend, in a great meafure, upon the com- 
preffibility and elafticity of it. There are feveral things that fecm 
to argue a confiderably greater denfity in the internal, than the ex- 
ternal part of the earth; and why may not this greater denfity be 
owing to the compreffion of the internal parts arifmg from the 
weight of the fuperincumbent matter, fince it is probable, that 
the matter, of which the earth is compofed, is pretty much 
of the fame kind throughout ? There is a ftill ftronger ar- 
gument for the earth’s owing its form, in fome meafure, to 
the fame caufe ; for it is found to be higher [fee the French 
accounts of the meafures of a degree of the meridian in France, 
Sweden, and America] at the equator, than at the poles, in a 
greater proportion than it would be on account of the centrifugal 
force, if it was of uniform denfity ; but, if we fuppofe the earth 
to be of lefs denfity in an equatorial diameter than in the axis, the 
whole will then be eafily accounted for, from the rifing.of the earth 
a little by its elafticity, the weight being in part taken off by the 
diurnal rotation : and that the earth is really a little denfer in the 
axis, than in the equatorial diameter, feems highly probable, from 
the experiments of pendulums compared with aftronomical obferva- 
tions ; for the forms of the earth derived from thefe, cannot be 
reconciled 
