to me a cause by no means alone adequate to the effect, which it is here suppos'd to produce.
For, if the Blood acts only as a weight by meer gravitation, then that part of it only which descends from the Parts above the Heart can be employ'd in that Action. This at the largest computation can't amount to Five pound weight, and must, according to the computation of Borellus, force a Machine, that is able to overcome a resistance of 135,000l. I leave every Man to deduct what he shall upon examination find reasonably to be deducted, and yet shall rest secure, that it is not to be effected in the least with so small a Weight.
But neither does the Refluent Blood gravitate in any such proportion, as I have here assign'd. For to make a true estimate of its Gravitation, we must consider the Circumstances of the Liquor suppos'd to gravitate; in which it very much resembles Water inclos'd in a recurve Tube, of which, if the length of the two Legs be equal, it may be suspended in the Air full of Water, with the Extremities downwards, without losing a drop, although the Diameter of those Legs should be very unequal. The Case of the Arteries and Veins is pretty near a parallel to a Tube, so fill'd and inverted. For, if the Arteries and Veins be continued Tubes, (as by the Microscope they are made to appear) then supposing their contents to have no other determination
of motion, than their own weight wou'd give them, the contain'd Fluids must be Counterpoises to each other. For the Veins and Arteries being join'd at the smaller Extremities, and the larger of both terminating in the same parallel Line, it is impossible, according to the Laws of Hydrostaticks, that the contents of either shou'd overbalance t'other. How far then must it fall short of forcing the natural Power and Resistance of so strong a Muscle as the Heart, by meer Gravitation?
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