Profefor WiL Liams on Earthquakes. 284 
an undulatory motion, like that of a wave ;, which firft rifes till 
it comes to its greateft height, and then fubfides ; and in fub- 
fiding, fpreads itfelf, with an horizontal motion, all around. 
This has appeared, with the moft fenfible evidence, to be the 
cafe, in all the earthquakes I have ever felt. They have all 
appeared, to me, to come on, as if a {olid body, or a wave of 
— earth, (if the expreffion may be allowed) was rolling along un- 
der the furface of the earth; which firft raifed that part which 
was over it, and then left it gradually to fubfide : the confe- 
quence of which was, a ftreng undulatory motion of the earth ; 
which was immediately fucceeded with an univerfal trembling, 
or very quick, jarring, vibratory motion, as though the earth 
was ftruggling to recover its former pofition. id: 
Another thing obfervable in the earthquakes of New-Eng- 
land is, they have all gone in much the fame cour/e. As to two 
or three of the earthquakes, we have no account of their cour/e : 
but in all thofe in which it was determined, there is a very 
great agreement. ‘They are all defcribed as coming from about 
north-weft, and going off about fouth-eaft. As this was the 
cafe with all whofe direction was obferved, we may rationally 
conclude, that they all proceeded in pretty much the fame ge- 
neral track ; in a path from about north-weft to fouth-eaft, 
though with many finall deviations and irregularities, in parti- 
cular places. This, if I do not miftake, has not been gene- 
rally the cafe in the earthquakes of other places. The great 
earthquakes which have fpread defolation in Sicily, Peru, and 
Sfamaica, inftead of proceeding in any regular courfe, are de- 
feribed rather as inftantaneous blafts, which.ftruck dreadfully 
upwards,—not proceeding in any certain tract, from one coun- 
try to another ; but fuch as burft and rent a large circle of earth 
