( 1225 ) 
But neither does the Refluent Uood gravitate many fucli 
proportion, as I have here affignd. For to make a true 
eftimate of its Gravitation^ we muft confider the circum- 
ftances of the Liquor fuppos'd to^ gravitate y in which it 
very much refembles Water inclos'd in a recurve Tube, of 
which, if the length of the two Legs be equal, it may be 
fufpended in the Air full of Water, with the Extremities 
downwards, without lofing a drop, altho the Diameter of 
thofe Legs fhou d be very unequal. The Cafe of the Arte- 
ries and Veins is pretty near a parallel to a Tube, fo fiird 
and inverted. For, if the Arteries and Veins be continued 
Tubes, ( as by the Microfcope they are made to appear ) 
then fuppofing their contents to have no other determinati- 
on of Motion, than their own weight woud give em, the 
contained Fluids muft be counterpoifes to each other. For 
the Veins and Arteries being joind at the fmaller extremi- 
ties, and the larger of both terminating in the fame Parallel . 
Line, it is impoffible, according to the Laws of Hydrojia- 
^^Vi-, that the contents of either (houd overballance t'other. 
How fat then muft it fallftiort of forcing the nataral Power 
and Refiftance of fo ftrong a Mufcle as the Heart, by meer 
Gravitation. 
The Blood indeed has a Progrejjive Motion thro its Vef- 
fels, wherein it differs from Water, in a recurve Tube, in 
the experiment above ftated. But, if the natural Gravita- 
tion of the Blood contributes nothing to the Dilatation of 
the Heart, this Progreffive Motion will not be found much 
more fufficient. For, as this Motion is deriv'd entirely from 
the Heart's Conftridion (as all accounts hitherto derive it) 
coud the Blood be fuppos'd to re-ad: upon the Heart, with 
all the force firft imprefs'd upon it by the Heart, it wou d 
be infufficient, unlets we will fuppofe the Force communi- 
cated to be fuperiour to the Vower Communicant^ which is 
abfurd. 
Bat when the juft and necelFary Dcdndions for the Im- 
pediments, which the Blood meets with in its Progrefs 
Dddddddd thro 
