286 PHILOSOPHICAL TRANSACTIONS. [ANNOI7I7. 



which it added to the whole weight of the fluid, when it ceases to be sustained 

 in it : contrary to M. Leibnitz's principle. 



Scholium. — If a cloud, by any cause whatever, become specifically heavier 

 than that part of the air in which it floats, the excess of its gravity above an 

 equal bulk of air will make it descend, and accelerate its motion downwards ; 

 and then indeed it will lose of its weight by the resistance of the medium, till 

 it comes to a uniform, or sensibly uniform motion : but all the weight that it 

 will lose, will only be the excess of its gravity above that of the air ; for with 

 the rest of its weight it will still make up part of the weight of the air. 



Exper. 1 . — Having With a weight in the scale c, fig. 3, of the balance ab, 

 counterpoised the long glass of water ei, with a horse-hair I let down the leaden 

 weight w into the water, which from fg rose up to eh ; and therefore the water 

 became heavier by the weight of a bulk of water equal to the lead. Having 

 with another weight in c made up the counterpoise to the whole, with fine 

 scissars I cut the thread of the plummet ; and all the while the plummet was 

 falling, the water descended rather than rose ; and when the lead was at the 

 bottom, the water overpoised, because it had then added to it all the excess of 

 the weight of the lead above an equal bulk of water, which by experiment is 

 about i^ of its weight. Had M. Reaumur and Ramazzini tried the experi- 

 ment in this manner, the success would have been the same; but M. Ramazzini 

 (as I was informed from a gentleman who was present) tried it in the following 

 manner, as I have since done. 



Exper, 1. — Using the same machine, after having balanced the water and 

 lead in it, I fixed to the end of the beam b, fig. 4, the thread of the plummet, 

 which in the former experiment I held in my hand. This added to the weight 

 hanging at b, and obliged me to put into the other scale a weight equal to 44 of 

 the lead, to recover the equilibrium. Then cutting the thread or hair, the 

 scale with the weights overpoised while the lead was falling; but the equilibrium 

 was restored when it came to the bottom. So that the lead even then must have 

 lost only its excess of weight above that of the water. 



Exper. 3, Jig. 8. — I tried the method proposed by M. Leibnitz in the follow- 

 ing manner. I took a cork c weighing an ounce, fig. 5, and somewhat more 

 than 4 times lighter than an equal bulk of water, and a ball of antimony w 

 about 4 times specifically heavier than water, and of 4 ounces weight. The 

 cork, laid upon the water in the vessel eabd, raised the water from ss to gg, 

 and added an ounce to the weight of the whole water: then suspending the ball 

 of antimony by a string, and letting it hang in the water at n, it raised the 

 water from gg to hh, and so added another ounce to the weight of the water. 

 Then tying the antimony to the cork (as in the figure 6, of the vessel marked 



