VOL. LI.] PHILOSOPHICAL TRANSACTIONS. • 451 



which it seems to have travelled at the rate of more than 20 miles per 

 minute. 



An historical account of the earthquakes which have happened in New Eng- 

 land says, that of 5 considerable ones 3 are known to have come from the same 

 point of the compass, viz. the north-west : it is uncertain from what point the 

 other 2 came, but it is supposed that they came from the same with the former. 

 The velocity of these has been much less than that of the Lisbon earthquakes: 

 this appears from the interval between the preceding noise and the shock, as 

 well as from the wave-like motion before-mentioned. All the greater earth- 

 quakes that have been felt at Jamaica seem, by the accounts given of them, to 

 have come from the sea, and, passing by Port-Royal, to have gone northwards. 

 The velocity of these also was far short of the velocity of the Lisbon earth- 

 quakes. The earthquake of London, on the 8th of March 1750, was supposed 

 to move from east to west. The same thing happened in a slight shock felt 

 there in the last century, as the person who told Mr. M. this, had an opportu- 

 nity of observing ; for being by accident in a scalemaker's shop at the time 

 when it happened, he found that all the scales vibrated from east to west. AH 

 the shocks that have been lately felt at Brigue, in Valais, have likewise come from 

 the same point of the compass, viz. the south. 



5thly, The Lisbon great earthquake has been succeeded by several local ones 

 since, the extent of which has been much less. 



Such were the earthquakes in Switzerland ; those on the borders of France 

 and Germany ; those in Barbary, &c. 



Sect. ii. — However well these facts may agree with the supposition before 

 laid down, that subterraneous fires are the cause of earthquakes, one doubt may 

 perhaps remain : viz. how it is possible that fires should subsist which have no 

 communication with the outward air ? In answer to this might be alleged the 

 example of green plants, which take fire by fermentation, when laid together in 

 heaps ; where the admission of the outward air is so far from being necessary, 

 that it will effectually prevent their doing so. But to pass by this, we have many 

 instances more immediately to the purpose. It can hardly be supposed that 

 the fires of the generality of volcanos receive any supply of fresh air (for this 

 must be effectually prevented by that vapour which is continually rushing out 

 at all their vents,) and yet they subsist, and frequently even increase, for many 

 ages. Now these are fires of the very same kind with those he supposes to be 

 the cause of earthquakes. Other facts, still more expressly to the purpose, are 

 as follow : 



In the earthquake of Nov. 1, 1/55, we are told that both smoke and light 

 flames were seen on the coast of Portugal, near Colares ; and that on occa- 

 sion of some of the succeeding shocks, a slight smejl of sulphur was perceived 



3 M 2 



