TOL. I-V.3 PHILOSOPHICAL TRANSACTIONS. 207 



that this loss of buoyancy was principally owing to the warmth the water had 

 got by standing in a warm room, as was hinted at before, which was further 

 proved by the thermometer ? a 



Exper. 8. A medal of lead, weighing one drachm when out of the wata^, 

 was found, on being weighed in river water, to be 54 grains and a half; being 

 less by 5 grains and a half than out of the water. The same medal being 

 weighed in the salt water was found to weigh 53 grains and a half. The differ- 

 ence between its hydrostatical weights being precisely one grain, or -^ more in 

 river water than in sea water. 



Exper. g. A phial of river water weighed exactly 82 grains; the same vessel 

 of sea water weighed exactly 84 ; the difference was two grains, or as 4 1 to 42. 



Exper. 10. After having made the foregoing experiments, with a view of 

 ascertaining the specific buoyancy of cork, and also the alteration it might 

 undergo from being immersed in river or sea water, we proceeded to the mor^ 

 important examen, to discover the precise quantity of cork necessary to sustain 

 a man in the water. For this end, 22 pieces of the best cork, such as is di- 

 rected to be used for the jackets, were provided; these were of different weightSj 

 from one ounce down to one scruple; so that by means of a string to which 

 they were occasionally fastened, one might easily learn what weight they would 

 suspend in the water, and what weight they would not suspend. This being 

 done, the next business was to find a proper person to make the experiment on; 

 for the accuracy of which it was judged proper to select a man of the smaller 

 size (as our seamen are seldom large) that was not very fat, because fat people 

 are more buoyant than lean or bony persons; one that could swim, that he 

 might go through the experiment with propriety, and without fear; one there- 

 fore was fixed on who was plump and muscular, not very bony, but moderately 

 so; his height was 5 feet 2 inches; his waist measured 2 feet 10 inches; his 

 weight was 104 pounds. Thus fitted out, he stripped naked, and 10 ounces of 

 cork being tied about his neck and breast, he committed himself to the river 

 Thames, near Chelsea, in a place where the water was about a foot below his 

 depth; but he could not keep his head above the surface without employing his 

 art, though he found not much art required to do it: another ounce of cork 

 was therefore added, and he perceived himself raised, so as now to be more able 

 to keep himself above the water, but yet he went slowly to the bottom, unless 

 he took care by swimming to prevent it. For this reason another ounce of 

 cork was applied, but still he sunk, though more slowly than before; and it was 

 plain to be observed, that the point between that maimer of sinking and swim- 

 ming was balanced with such extreme nicety, that the smallest addition of co;k 

 would determine in favour of buoyancy : accordingly half an ounce was added, 

 and this weight supported him in a vibrating state; but by the superaddition of 



