80 HISTORY OF 



geveiitietli part of the way. The air, therefore, at the centre, 

 must be infinitely heavier than mercury, or any body that we 

 know of. This granted, we shall take something more, and 

 say, that it is very probable there is nothing but air at the centre. 

 Now let us suppose tiiis air heated, by some means, even to the 

 degree of boiling water, as we have proved that the density of 

 the air is here very great, its elasticity must be in proportion •, 

 a heat, therefore, which at the surface of the earth would have 

 produced but a slight expansive force, must, at the centre, pro- 

 duce one very extraordinary, and, in short, be perfectly irresis- 

 tible. Hence this force may, with great ease, produce earth- 

 quakes ; and if increased, it may convulse the globe ; it may 

 (by only adding figures enough to the calculation) destroy the 

 Bolar system, and even the fixed stars themselves." These re- 

 veries generally produce nothing ; for, as I have ever observed, 

 increased calculations, while they seem to tire the memory, give 

 the reasoning faculty perfect repose. 



However, as earthquakes are the most formidable ministers 

 of nature, it is not to be wondered that a multitude of writers 

 have been curiously employed in tlieir consideration. Wood- 

 ward has ascribed the cause to a stoppage of the waters below 

 the earth's surface by some accident. These being thus accu • 

 mulated, and yet acted upon by fires, which he supposes still 

 deeper, both contribute to heave up the earth upon their bosom. 

 This he thinks, accounts for the lakes of water produced in an 

 earthq\iake, as well as for the fires that sometimes burst from 

 the earth's surface upon those dreadful occasions. There are 

 others who have supposed that the earth may be itself the cause 

 of its own convulsions. " When," say thoy, " the root or basis 

 of some large tract is worn away by a fluid underneath, the earth 

 sinking therein, its weight occasions a tremor of the adjacent 

 parts, sometimes producing a noise, and sometimes an inu^da- 

 tion of water." Not to tire the reader with a history of opinions 

 instead of facts, some have ascribed them to electricity, and 

 some to the same causes that produce thunder. 



It would be tedious, therefore, to give all the various opinions 

 that have employed the speculative on this subject. The ac- 

 tivity of the internal heat seems alone sufficient to account for 

 every appearance that attends these tremendous irregulari- 

 ties of natm-e. To concoivc this distinctly let us suppose 



