6io Mr. mann’s ! Treatife 
S3. 27. 28. 29.). But from the moment that part of 
this water overflows the bed, the velocity thereof begins 
to diminifh (N° 41.) and does fo more and more, the 
farther it flows and fpreads on the plain. So that the 
overflowing being once begun, it is a natural confe- 
quence, that the inundation lliould continue for feveral 
days; for though the volume of water brought down by 
the flood during that time fhould decreafe, yet, as the 
quantity of what runs off decreafes likewile, from the 
great decreafe of velocity in what overflows the plains, 
it will continue to produce the fame effect as if the vo- 
lume of water coming down had not diminifhed, until 
the whole of the ftream be every where contained again 
within the bed of the river. When that is become the cafe, 
the waters that have overflowed the plain will decreafe 
thereon, by gradually and flowly running off, and alfo by 
evaporation, till they wholly difappear. If this was not 
fo, we fhould fee rivers overflow for an hour or two, 
and then return again within their beds, a thing con- 
trary to general obfervation ; for we conftantly fee inun- 
dations, once begun in flat countries, laid for feveral days 
together, although in the mean while the rain ceafes, 
and the quantity of water coming down diminifhes. This 
muft be the cafe, becaufe as the overflowing diminifhes 
the velocity, and confequently the quantity of water 
carried 
