[ 630 3 
not in the fame proportion with the diftances of the 
refpe&ive places from the fuppofed fource of the 
motion ; this, however, is no objection againft the 
point alfumed, fince it is manifeft, wherever it was, 
that it could not be far from Lilbon, as well becaufe 
the wave arrived there fo very foon after the earth- 
quake, as becaufe it was fo great, riling, as -we are 
told, at the diftance of three miles from Lilbon, to 
the height of fifty or fixty feet. The true reafon of 
this difproportion, feems to be the difference in the 
depth of the water ; for, in every inftance in the above 
table, the time will be found to be proportionably 
fhorter or longer, as the water through which the 
wave palTed was * deeper or lhallower. Thus the 
motion of the wave to Kingfale or Mountlbay (through 
waters not deeper in general than aoo fathoms) was 
flower than that to Madeira, (where the waters are 
much deeper) in the proportion of about three to 
five ; and it was flower than that to Barbadoes, 
(where its courfe lay through the deepell part of the 
Atlantic ocean) nearly in the proportion of one to 
three : fo likewife the motion of it from the Scilly 
illands to Swanfea in Wales (where the depth gra- 
dually diminilhes from about fixty or feventy fa- 
thoms to a very fmall matter) was If ill flower than 
that to Kingfale, in the proportion of lefs than one 
to three : the fame thing is obfervable with regard to 
* We have an inftance to this purpofe in the tides, which, in 
deep waters, move with a velocity that would carry them round 
the whole earth in a Tingle day; but as they get into fhallowcr 
waters, they are greatly retarded : and we are told, that in the 
river of Amazons, the fame tide is found running up to the tenth 
or twelfth day, before it is entirely fpent. [See Condamint s Voyage 
down the Mara non.] 
Plymouth 
