Chap. 3. PHILOSOPHICAL DISCOVERIES. 71

times greater than its resistance in water. This is the leastresistance such a ball could meet with; in. a plenum , should! weallbw the-suppositions that are most favourable in this doctrine ;>and this resistance would’ soon put. an end to the motions ofbodies. But it is evident that we allowed too much in. savourof their doctrine, when we supposed, the ball moving in thequick silver to meet with a resistance equal to the sum. of theresistances that it would meet with from the plenum and quicksilver separately. For, according to this supposition, its re-sistance in quick silver would be to its resistance in water, asthe turn- os the densities of gold and quick silver to the sum; ofthe densities os gold and water, that is, as 335 to 205, or 67to 41 ; so that the resistance of quick silver would not bedouble of that of water, or even double of that of air ; thanwhich nothing can be more contradictory to experiment.

It is of no importance to this argument how rare gold,quick silver, or the heaviest bodies, be supposed; since theresistance os quick silver in fact is known to be very great,and is not altered by such suppositions : neither is the pro-portion of the density of gold to that of quick silver (uponwhich proportion the argument is sounded) affected by them.For it will always be found that the resistance of a golden ballin a plenum (how freely soever it pass through the pores of theball, and how large or numerous soever these pores may be)must correspond to the solid matter in the ball ; which isgreater than the solid matter in any equal bulk of any of ourfluids ; upon which their resistance depends. The supposingthe solid matter in the quick silver to occupy only the thou-sandth or millionth part of its bulk, has no other effect butthat it supposes the inertia of a given quantity of solid matterto be increased in the same proportion with the rarity os the:quick silver, whose inertia is in fact ascertained.

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