284 Profifor Wiattikw on Earthquakes. 
fhock. The reverfe has been the cafe in the earthquakes: öf 
New-England. Inftead of being inftantaneous; their motion. 
has never been very fwift.. To compute, indeed, with accu- 
racy, with what velocity any of them: moved, we have no fuf- 
ficient deta. Had the times at which afty of them begun, been 
carefully noted at places whofe diftances were known, it might 
have operied the way to fome very curious conclufions. But 
all the accounts, excepting one of Profeflor Winthrop, are too 
general to form any certain inferences of this kind. There is, 
‘however, one article in the accounts of the earthquakes of 
1727, 1755, 1757 and 1761, from whence we may conclude, 
that the velocity of their motion, was confiderably lefs than that 
of JGund. Moft of the accounts of the earthquakes of 1727 and 
1755, agree, that the roar was heard at leaft half a minate be- 
fore the thake began. The found, therefore, that was occai 
fioned by the approach of the earthquake, préceded the fhock 
. with a motion. confiderably fwifter than that of the — 
itíelf. Now, found moves about thirteen miles in a minute ; 
and the motion of this was confiderably fwifter than the mo- 
tion of theearthquake. In the earthquakes of 1757 and 1761, 
» the found was alfo heard half a minute before the fhock was 
felt : and as the report was much lefs, and therefore could not 
‘reach fo faras in the larger fhocks, the inference will be, that 
thefe fmall fhocks moved with a velocity confiderably lef than 
‘the larger one. And, indeed, the fuppofition fems not im- 
. probable, ‘that the vebcity with which an earthquake moves, 
—fhould bear fome proportion to its violence,-—to- the ftrength 
“and force of "thofe Galles, by whofe i operation it is produced. 
Whether there: dots not feern fome evidence that thf hasbeen 
the cafe With s, ‘the Header Will judge for himéelf, from what 
has 
