Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/216

 contrary term, another intrinsick and natural quality, which maketh it averse to motion. Therefore tell me again; do you not think that the inclination v. g. of grave bodies to move downwards, is equal to the resistance of the same to the motion of projection upwards?

I believe that it is exactly the same. And for this reason I see that two equal weights being put into a ballance, they do stand still in equilibrium, the gravity of the one resisting its being raised by the gravity wherewith the other pressing downwards would raise it.

Very well; so that if you would have one raise up the other, you must encrease the weight of that which depresseth, or lessen the weight of the other. But if the resistance to ascending motion cunsist onely in gravity, how cometh it to passe, that in ballances of unequal arms, to wit in the * Stiliard, a weight sometimes of an hundred pounds, with its pression downwards, doth not suffice to raise up on of four pounds; that shall counterpoise with it, nay this of four, descending shall raise up that of an hundred; for such is the effect of the pendant weight upon the weight which we would weigh? If the resistance to motion resideth onely in the gravity, how can the arm with its weight of four pounds onely, resist the weight of a sack of wool, or bale of silk, which shall be eight hundred, or a thousand weight; yea more, how can it overcome the sack with its moment, and raise it up? It must therefore be confest Sagredus, that here it maketh use of some other resistance, and other force, besides that of simple gravity.

It must needs be so; therefore tell me what this second virtue should be.

It is that which was not in the ballance of equal arms; you see then what variety there is in the Stiliard; and upon this doubtlesse dependeth the cause of the new effect.

I think that your putting me to it a second time, hath made me remember something that may be to the purpose. In both these beams the business is done by the weight, and by the motion; in the ballance, the motions are equal, and therefore the one weight must exceed it in gravity before it can move it; in the stiliard, the lesser weight will not move the greater, unless when this latter moveth little, as being hung at a lesser distance, and the other much, as hanging at a greater distance from the lacquet or cock. It is necessary therefore to conclude, that the lesser weight overcometh the resistance of the greater, by moving much, whilst the other is moved but little.

Which is as much as to say, that the velocity of the moveable less grave, compensateth the gravity of the moveable more grave and less swift.