284 PHILOSOPHICAL TRANSACTIONS. [aNNO l?!/. 



naturally be applied to the above-mentioned particles of water ; they increase 

 the weight of the air when it sustains them, which is diminished when it lets 

 them fall : and as it may often happen that the particles of water that are 

 highest, fall a considerable time before they join with those that are low, the 

 gravity of the air diminishes before it rains, and the barometer shows it." 



" This new principle of M. Leibnitz is surprising. For must not a strange 

 body, whether sustained in a liquid or not, always weigh ? Can it gravitate on 

 any other bottom than that which sustains the whole fluid ? Does that bottom 

 cease to carry a strange body, because it falls ? And is not that body all the 

 while it is falling, part of the said liquid as to the weight? At that rate, whilst 

 a chemical precipitation is made, the whole matter ought to weigh less, which 

 has never been observed, and scarcely appears credible." 



" Notwithstanding these objections the principle holds good, when more 

 closely examined. What sustains a heavy body is pressed by it. A table, for 

 example, which sustains a pound weight of iron, is pressed by it, and is so only 

 because it sustains the whole action and effect of the cause of gravity, whatever 

 it be, to push that lump of iron lower. If the table should yield to the action 

 of that cause of the weight, or gravity, it would not be pressed, and therefore 

 would carry nothing. After the same manner the bottom of a vessel, which 

 contains a fluid, opposes itself to all the action of the cause of gravity against 

 the said fluid : if an extraneous body float in it, the bottom opposes itself also 

 to the said action against that body, which, being in equilibrio with the fluid, 

 is in that respect really a part of it. Thus the bottom is pressed both by the 

 fluid and the extraneous body, and it sustains them both. But if the body 

 fall, it yields to the action of gravity, and consequently the bottom no longer 

 sustains it ; neither will it sustain it, till the said body is come down to the 

 bottom. Therefore during the whole time of the fall, the bottom is eased of 

 the weight of that body, which is no longer sustained by any thing, but pushed 

 down by the cause of gravity, to which nothing hinders it from yielding." 



" M. Leibnitz, to confirm his notion, proposed an experiment. He says, 

 that two bodies must be tied to the two ends of a thread, the one heavier, and 

 the other lighter than water, yet such as both together may float in water: put 

 them into a tube full of water, the tube being tied to one end of the beam of 

 a balance whose other end has a counterpoising weight : then if we cut the 

 thread which ties the bodies together, that are of unequal weight, so that the 

 heaviest may presently descend, he says, that in such a case the tube would be 

 no longer in equilibrio, but its counterpoising weight would preponderate, be- 

 cause the bottom of the tube would be less pressed. It is plain that the tube 

 must be sufiiciently long, that the falling body may not reach the bottom be- 

 fore the tube has time to rise. In chemical precipitations, the vessels are either 



