upon the Phenomena, of Earthquakes. 269 
represented bv the following experiment. Suppose a large cloth, 
or carpet, (spread upon a floor) to be raised at one edge, and 
then suddenly brought down again to the floor, the air under it, _ 
being by this means propelled, will pass along, till it escapes at 
the opposite side, raising the cloth in a wave all the way as it 
goes. In like manner, a large quantity of vapour may be con- 
ceived to raise the earth in a wave, as it passes along between 
the strata, which it may easily separate in an horizontal direc- 
tion, there being, as I have said before, little or no cohesion be- 
tween one stratum and another. ‘The part of the earth that is 
first raised, being bent from its natural form, will endeavour to 
restore itself by its elasticity, and the parts next to it beginning 
to have their weight supported by the vapour, which will insi- 
nuate itself under them, will be raised in their turn, till it either 
finds some vent, or is again condensed by the cold into water, 
and by that means prevented from proceeding any further. 
99. If a large quantity of vapour should continue to be gene- 
rated for some time, several waves might be produced by it; and 
this would be, in some measure, the case, if the quantity at first 
generated was exceedingly great, though the whole of it was 
generated in less time, than whilst the motion was propagated 
through the distance between two waves. 
60. These waves must rise the higher, the nearer they are to 
the place from whence they have their source; but, at great di- 
stances from thence, they may rise so little, and so slowly, as not 
to be perceived, but by the motions of waters, hanging branches 
in churches, &c. . 
61. The vibratory motion occasioned by the first impulse of 
the vapour, will be propagated through the solid parts of the 
earth, and therefore, it will much sooner become too weak to be 
perceived, than the wave-like motion; for this latter, being oc- 
casioned by the vapour insinuating itself between the strata, 
may be propagated to very great distances ; and even after it has 
ceased to be perceived by the senses, it may still discover itself 
by the appearances before mentioned. 
' Section IV.—62. All earthquakes derived from the same sub- 
terraneous fire, must come to the same place in the same direc- 
tion; and those only which are derived from different fires, will 
come from different points of the compass; but as, in all pro- 
bability, it seldom happens that earthquakes, caused by different 
fires, affect the same place, we therefore find in general, that 
_ they come from the same quarter: it is not, however, to be sup- 
posed, that this should always be the case, for it will, probably, 
sometimes happen to be otherwise: and this is to be expected 
in such places as are situated in the neighbourhood of several 
subterraneous 
