contrary, in Rivers, at any confiderable diftance from tlie 
Sea, the refiftance of the weight of the frefli Weter, which h 
tept fulpended during the tirne of the Flood, is longer over- 
Came by the more potent Impetiis in the New and Full, than 
by the weaker in the ^adratures: and from hence this dif- 
ference fliould be ftili more and more confiderable as the 
Port is farther removed from the Sea. 
A Demonflration of the Velocity wherewith the Air rnjhes 
into an Exhaujied Kecei^er^ lately produced before 
the R. Society by Dr. D. Papin. Reg. Soc, S« 
THere being feveral Occafions wherein it would be ufe- 
ful to know the Velocity of the Air, according to the 
leveral prejOTures that may drive it ; The Royal Academy at 
Tar is hath attempted by fbme Tryals to attain that Know- 
ledg, and by means of a Bladder,, which they did fometimes 
fill up with Water^ and fometimes with Air ; they found 
that (altliough the Weight to fqueeze out thefe Liquors^ 
and the hole to let them out were the fame) nevertlielefs, 
the Bladder when full of Air, could be emptyM in the 2 5^^. 
part of the time that was required to fqueeze out the Water 
of the lame Bladder : from thence they concluded that the 
fwiftnefi of the Air is 2 5 times greater than that of water, 
when both thefe hquofs bare the fame preifure. ThisEjc- 
perimentwas very well thought on, and might ferue till a 
better fhould be found out y but thofe Gentlemen could not 
but know, that tliis was not Perfect : The Reafon is that 
the Air yieldeih mucli, and so the Bladder being filfd with 
it,, will become pretty flatt, as fbon as a confiderable weight 
is layd upon it. It is plain therefore that the weight bearing 
upon a large fpace doth not prefs euery part with the fame 
force as it would do, if the Bladder did for a while remam 
Plump, as it doth when full f water : moreouer, the water 
it felf being heauy in the Bladder, makes ibme preffure: fo 
A a 2 that 
