268 Conjectures concerning the Cause, and Observations 
fissures, immediately communicating with the hollow left by the 
part that fell in, must run out upon the fire, the steam taking 
its place. From hence may be generated a vast quantity of va- 
pour, the effects of which shall be considered presently. This 
steam will continue to be generated, supposing the fire to be 
sufficiently great, till the fissures before mentioned are evacuated, 
or till the water begins to flow very slowly; when the steam al- 
ready formed will be removed by the elasticity of the earth, which 
will again subside, and, pressing upon the surface of the melted 
matter, will force it up a little way into all the clefts, by which 
the water might continue to flow out. By this means, all com- 
munication between the fire and the water will be prevented ex- 
cepting at these clefts, where the water, dripping slowly upon 
the melted matter, will gradually form a crust upon it, that will 
soon stop all further communication in these places likewise ; 
and the fissures, that had been before evacuated, will be again 
gradually replenished by the oozing of the water between the 
Strata. y 
58. As a small quantity of vapour almost instantly generated 
at some considerable depth below the surface of the earth, will 
produce a vibratory motion, so a very large quantity (whether it 
be generated almost instantly, or in any small portion of time) 
will produce a wave-like motion. The manner in which this 
wave-like motion will be propagated, may, in some measure, be 
greater density be owing to the compression of the internal parts arising 
from the weight of the superincumbent matter, since it is probable, that 
the matter, of which the earth is composed, is pretty much of the same kind 
throughout? ‘here is a still stronger argument for the earth's owing its 
form, in some measure, to the same cause; for it is found to be higher [see 
the French accounts of the measures of a degree of the meridian in France, 
Sweden, and America] at the equator, than at the poles, in a greater pro- 
portion than it would be on account of the centrifugal force, if it was of 
uniform density ; but, if we suppose the earth te be of less density in an 
equatorial diameter than in the axis, the whole will then be easily accounted 
for, from the rising of the earth a little by its elasticity, the weight being in 
part taken off by the diurnal rotation: and that the earth is really a little 
denser in the axis, than in the equatorial diameter, seems highly probable, 
from the experiments of pendulums compared with astronomical observa~ 
tions; for the forms of the earth derived from these, cannot be reconciled 
with each other, but upon this supposition, [See Maclaurin’s Fluxions, 
art. 681, &c.] It appears, from some late and accurate observations, that 
the equatorial parts of the planet Jupiter also, as well as those of the earth, 
are a little higher than they weuld be, if their rise was owing to the cen- 
trifugal force, and he was of uniform density; but if we suppose him to be 
of less density in the equatorial, than the polar regions, then the form may 
be such as he would assume from the respective gravitation of the several 
parts; and any fluid like our ocean, would not overflow the polar parts, 
(which, upon any other supposition, it must mecessarily do,) but would fol- 
low his general form, as our ocean does that of the earth. 
represented 
