VOL. XIII.J PHILOSOPHICAL TRANSACTIONS. GSQ 



three years; which, together with a remarkable calmness of the air, a matter 

 generally considered as one of the circumstances which accompany earthquakes, 

 and by many reckoned among the signs which precede them, may be sufficient 

 to show how free the air was from vapours at that time; and surely the fewer 

 there were above, the more may be supposed below. Ignes fatui were fre- 

 quently seen a few days before the earthquake; which may be a probable argu- 

 ment, at least, to show how full the earth was then of damps and exhalations; 

 since a stench, that tainted well water after an unusual manner, has on the 

 same account been generally reckoned amongst the signs of an earthquake, and 

 by which it may be predicted : for by this it was that Pherecydes is said to have 

 presaged the earthquake of Lacedemon ; and Helmont mentions another who 

 pretended to the same foresight, by tasting the water of a very deep well in the 

 castle of Lovain. 



The motion of this earthquake was not of that sort which are termed pulses 

 or succussions; such as strike the ground at right angles with a violent shock, 

 or intermittent knocking, so as to raise the earth to a considerable height, or 

 force their way by a breach ; but it appears rather to be such a trembling motion, 

 as vibrates and shakes, without altering the position of the earth, and leaves 

 all things in the same posture in which it found them. For it shook the earth 

 with a tremulous and vibrating motion, whose reciprocations were repeated 

 with great quickness. The pulses were a little discontinued, and yet they came 

 so thick that I could not count them, though the whole earthquake continued 

 here scarcely more than 6 seconds of time; and when that ended, the restoring 

 motion, or settling of the building in which I was, seemed to be with a crash. 



Now as tremulous and vibrating motions are proper to produce sounds, so 

 was this earthquake accompanied with a hollow murmuring sound, like distant 

 thunder; which sound kept time so exactly with the motion, and was so con- 

 formable to it in all respects, that it plainly appears there was the same cause 

 for both. To those that were within doors, it appeared to be more consider- 

 able, and as it were in the air above, occasioned chiefly by the shaking of the 

 building. But those that were abroad in the fields and open air, perceived, 

 with a gentle shaking, a hollow murmur towards the surface of the earth, not 

 unfitly compared to the groaning of some planks of elm, ash, or fir, when the 

 application of fire to the wood causes both a trembling and sound. 



That there is considerable heat within the earth, is manifest, from the 

 experience of miners working in the deeper grooves, from those hot springs 

 which break out thence, and from fermentations occasioned by mineral spirits, 

 &c. Nor is it less commonly observed, that such heats and fermentations 

 within the earth are augmented by frosty weather ; when the steams being more 



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