VOL. LV.] PHILOSOPHICAL TRANSACTIONS. 205 



river water, with which it was nearly saturated at the time of its immersion in 

 the sea water. — After an immersion of 48 hours in the salt water, this float (a) 

 lost ]6 grains of its buoyant power; and having been 72 hours in the salt water, 

 on weighing it again out of the water, being wiped, but full of water, it was 

 found to weigh 24 1 grains, having gained 30 grains* After being Q hours out 

 of the water, in a dry room, it weighed 213 grains, having lost 28 grains. 

 This float (a) having been 76 hours in the salt water, in which it then sustained 

 949 grains of lead, was removed, thus saturated with the sea water, into a vessel 

 of fresh river water, and was found to sustain 923 grains only, being 26 grains 

 less than it bore up in the salt water ; and yet it must be observed, that this float 

 had been saturated with fresh water before it was immersed in the salt water. 



Exper. 5. Not content merely to know the buoyant power of cork in fresh 

 water, it was next tried in sea water. Five cubes, being each an inch square on 

 every side, made of the best sound compact cork, with distinct gauges made of 

 cork, and adjoining, as in the preceding experiments, were prepared, each 

 weighing as annexed; these being united, formed . 



one float (marked b) that they might the nearer 2 42J 

 resemble the texture of the cork jacket. A ves- 3 ^^ 

 sel of sea water taken up near the North Fore- 5 43 

 land being: then provided, the float was found to 



. • •. 1 J J 11- • L- ,^.r. Sum 234* 



support m it a leaden medallion weighing 1048 



grains. When it had continued in the sea water for 48 hours, it exactly sup- 

 ported 1024 grains, having, by being in the salt water, for that space of time 

 lost 24 grains of its buoyant power. 



From this experiment we learn, that the salt water insinuates more into the 

 substance of cork than fresh water does, which may perhaps be attributed to its 

 oiliness, oil being more subtil and penetrating, than water; it could not there- 

 fore be expected that the cork should retain its force so vigorously, for so long a 

 time as in the fresh river water; and, on weighing, it was found to lose -^ of its 

 buoyancy in 48 hours. But then we are further to observe that the sea water 

 supports a greater weight, and gives nrore buoyancy to the cork float than fresh 

 water, in the proportion of 353 to 339; for a float weighing 44 grains, support- 

 ing 353 grains of lead in fresh water, buoyed up 359 grains of lead in the sea 

 water, being more by 6 grains. And it is to be noted, that the sea water taken 

 up at the North Foreland is not so much impregnated with the marine principles, 

 as that which is taken up at a greater distance from fresh water rivers, which 

 decreases in its buoyancy in proportion to its vicinity to or mixture with rivers; 

 for on evaporating, it yielded only 2 drachms and 1 grain of salt to a pint, 

 which is less by 7 grains than is yielded by that taken up at the Isle of Wight. 



Exper. 6. The float b being continued in immersion in salt water for 72 



