VOL. VII.] PHILOSOPHICAL TRANSACTIONS. 43 



having continued there for some time, they would again emerge. And though 

 sometimes they would rise to the top or fall to the hottom of the water, accord- 

 ing as the air was hot or cold ; yet it was not difficult to distinguish those mo- 

 tions from those produced by the varying gravity of the atmosphere. For when 

 the beams of the sun, or heat of the ambient air, by rarefying the air included 

 in the bubbles, made that air drive out some of the water, and consequently 

 made the whole bubble (consisting of glass, air and water) somewhat lighter 

 than a bulk of water equal to it, though the bubble did necessarily swim as long 

 as the included air was thus rarefied, yet when the absence of the sun, or any 

 other cause made the air lose its adventitious warmth, there would ensue a 

 condensation of the air again, and thereupon an intrusion of more water (to 

 succeed the air) into the glass, and consequently a sinking of the bubble : and 

 this would commonly happen at night, if it did not happen sooner. But when 

 it was upon the account of the varying weight of the atmosphere that the bub- 

 bles either rose or fell, it appeared by the baroscope, that the atmosphere was 

 so heavy or so light, that they ought to do so. Insomuch that I divers times 

 predicted, whether I should find the mercury in the baroscope high or low, by 

 observing the situation and posture of the bubbles ; and consulting that instru- 

 ment, it verified my conjectures. 



N.B. 1. It being very difficult to poise several bubbles precisely, as well one 

 as another, I thought it not strange, that all the three bubbles did not con- 

 stantly rise and fall together, but sometimes two of them, and now and then 

 one alone would sink or emerge, when the change of the weight of the atmos- 

 phere was not considerable enough to operate sensibly upon the rest. And 

 therefore it is not amiss, to poise a greater number of bubbles together, that, 

 after trial made of all, the fittest may be chosen. 



2. I have observed it sometimes to happen, that a bubble, that floated when 

 it was first poised, would after a while subside without any manifest cause; or 

 if it were made to sink by such a cause, it would continue at the bottom of the 

 water, though that cause were removed : which difficult phenomenon seeming 

 to depend upon a kind of imbibition made of certain particles of an aerial na- 

 ture by the water, the consideration of it belongs to another place, not to this; 

 where it may suffice, that the experiment did sometimes actually answer ex- 

 pectation as that above related did ; wherein my main drift was to show, that 

 since, as the atmosphere is heavier or lighter, it is capable of working upon 

 bodies under water so as to procure their sinking, or their emersion ; the air 

 (though a fluid a thousand times lighter) must lean or press upon the water it- 

 self, by whose intervention it produces these effects ; which confirms what I 



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