will with its whole weight bear upon and preſs the middle part towards the other extreme part EGF; and therefore the force with which EGI, the ſum of the parts HKI and EGKH, tends towards the third part EGF, is equal to the weight of the part HKI, that is, to the weight of the third part EGF. And therefore the weights of the two parts EGI and EGF, one towards the other, are equal, as I was to prove. And indeed if thoſe weights were not equal, the whole earth floating in the nonreſiſting aether would give way to the greater weight, and, retiring from it, would be carried off in infinitum.
And as thoſe bodies are equipollent in the congreſs and reflexion, whoſe velocities are reciprocally as their innate force: ſo in the uſe of mechanic inſtruments, thoſe agents are equipollent, and mutually ſuſtain each the contrary preſſure of the other, whoſe velocities, eſtimated according to the determination of the forces, are reciprocally as the forces.
So thoſe weights are of equal force to move the arms of a Ballance, which during the play of the ballance are reciprocally as their velocities upwards and downwards: that is, if the aſcent or deſcent is direct, thoſe weights are of equal force, which are reciprocally as the diſtances of the points at which they are ſuſpended from the axis of the ballance; but if they are turned aſide by the interpoſition of oblique planes, or other obſtacles, and made to aſcend or deſcend obliquely, thoſe bodies will be equipollent, which are reciprocally as the heights of their aſcent and deſcent taken according to the perpendicular; and that on account of the determination of gravity downwards.
And in like manner in the Pully, or in a combination of Pullies, the force of a hand drawing the rope directly, that is to the weight, whether aſcending directly or
