IMPROVED. 59 



Poflulates, rather than the Infufficiency of the Means 

 he made ufe of: For Dr. Keil has fmce^ by the 

 fame Helps from Geometry, much more fatisfadlo- 

 rily determined it. For if we have the Velocity 

 wherewith a Fluid flows out at any Orifice, with- 

 out Refiftance from an anterior Fluid, it is eafy to 

 determine the Force which produces that Motion. 

 But this would, at prefent, take up too much Time 

 to perform. 



The Hearts of any Creatures are to one another 

 as their Weights ; and it is computed, that the 

 Weight of (I mean the ordinary Weight) a human 

 Heart is twelve Ounces, then its Force will be al- 

 moft = eight Ounces : And although this Compu- 

 tation be fomewhat more than has been formerly 

 determined, yet it is of no great Moment, if we 

 Confider Borelli^s, who required a Force in the 

 Heart's PrefTure = 180000/1^. Weight, to move 

 7.0 lb. of Blood: But this great DifSrence of his 

 Calculation feems to arife from his not diftinguifh- , 

 ing between the Blood at Reft and already in Mo- 

 tion : For, the Force of the Heart is not employed 

 in moving any Quantity of Blood at Reft, but only 

 to continue it in Motion. Yet how this Motion 

 firft came, or was imprefs'd upon it, feems out of 

 human Capacity to determine. However, this is 

 certain, that if the Refiftance of the Blood bore 

 always the fame Proportion to the Force of the 

 Heart, as it does now, the Blood never could at firft 

 be put in Motion by the Heart ; for there is a vaft 

 Difproportion between moving a Body at Reft, and 

 keeping it in Motion when it has acquired it. This 

 k difcoverable, in a very eminent Degree, in the Flux 

 and Reflux or Flowing and Ebbing of the Sea; for, Jhe Rea- 

 the higheft Tides are not precifely on the New and Full f?" 1;^^ ^ 



00ns, nor the N caps on the Quarters : But general- ^ idts are 

 ly, they are the thirdTidesafier them, andfometimesnor pre- 

 later; and the Reafonis, that the Water's being put in <^if*-'iy ^'P- 

 Motion by the Aftion of the Luminaries, their Li-^cha^'e^ 

 bration or fwinging in the Manner of a Pendulum ^^ the^"^^ 



continues Muon, 



