SUMATRA. 
tity, prefles on the ground, whofc reaction caufes ic to rufli on in that 
manner which wc call a furf. Some think that the peculiar form of 
it, may be plainly accounted for, from the ihallownefs and Ihelving of 
the beach. When a fvvell draws near to fuch a beach, the lower parts 
of the water meeting firfl with obftrudion from the bottom, Itand ilill, 
whild the higher parts refpedively move onward; by which a roiling 
and involved motion is produced, that is augmented by the return of the 
preceding fwell. I object that this folution is founded on the fuppofi-^ 
tion of an adlual progrefTive motion of the body of water in forming a 
furf I and that certainly not being the fad. It feems deficient. The only 
real progrcflion of the water is occafioncd by the perpendicular fall^ 
after the breaking of the furf, when, from its weight, it foams on to a 
greater or lefs diftance, in proportion to the height from which it feU, 
and the Hope of the fhore. 
That the furfs are not, like common waves, the immediate e fifed of 
the wind, is evident from this, that the higheCl and moft violent 
often happen when there is the leaft wind, and vice vsrfd* Andfome- 
times the furfs will continue with an equal degree of violence daring 
a variety of weather. On the weft coaft of Sumatra, the higheft are 
experienced during the S, E. monfoon, which is never attended with 
fuch gales of wind as the N. W* The motion of the furf is not 
obferved to follow the courfe of the wind, but often the contrary ; 
and when it blows hard from the land, the fpray of th<» may be 
feen to Jly in a aireaion oppolite to the body of it i though the wind 
has been for many hours in the fame point. 
Are the furfs the effedof gales of wind at fea, which do not happen 
to extend to the ihore, but catafe a violent agitation throughout a con- 
fiderable trad of the waters, which communicating with lefs diftant 
parts, and meeting at length with refiflance from the fhore, occafions the 
fea to fwell and break in the manner defcribed ? To this I objed, that 
there feems no regular correfpondence between their magnitude, and 
the apparent agitation of the water without them ; that gales of wind, 
except 
