204 PHILOSOPHICAL TRANSACTIONS. [aNNO 1765. 



XFI. A Course of Experiments to ascertain the Specific Buoyancy of Cork in 

 different fVaters : also. The respective Weights and Buoyancy of Salt Water 

 and Fresh Water : andfor determining the exact Weight of Human and other 

 Bodies in Fluidi. By John Wilkinson, M. D., F. R.S. p. 95. 

 Exper. 1 . Six cubes of good cork, each mea- 

 suring an inch square, as nearly as they could 

 possibly be ascertained, with a graduated gauge 

 of cork fastened to a point of each, severally 

 weighed as in the statement annexed ; the me- 

 dium weight being the exact weight of a cubic „^ ^177 

 inch of cork, is nearly 46^. 



Exper. 1. N" 1, 2, 3, 4, formed a float named a, being IQO grains of cork, 

 which was fastened to a medallion of lead, weighing 1 ounces, by a wire that 

 weighed 8 grains ; these being put into a deep jar of Thames water, taken above 

 the new bridge, the lead weighed exactly 4J grains; so that 19O grains of cork 

 supported precisely 916 grains of lead in river water. 



Exper. 3. The float was left in the same water, immersed by the medallion 

 for the space of 48 hours, with a view of obtaining a precise knowledge of the 

 quantity of water the cork might imbibe; also how its buoyancy might be 

 affected; and how much extension it might acquire from a certain continuance 

 under the water. It was somewhat surprising to find, that after this period of 

 immersion the cork had not, as might have been expected, lost any force of 

 buoyancy; but on the contrary, it had actually gained 2 grains, and was found 

 to support 91 8 grains of lead: which must be attributed, it maybe presumed, 

 to an expansion of the air contained in the cork, acquired from its immersion in 

 the fresh water. 



To be further informed how cork would be affected by a continued immersion, 

 the same float, after weighing, was again immersed in the same water, for the 

 space of 48 hours longer. And now the water was found to have penetrated its 

 recesses and cavities, insomuch that its buoyancy had decreased 1 1 grains, and it 

 then supported only 905 grains. This decrease may possibly be attributed to a 

 greater imbibition in the cork, and a greater penetration given to the water, by 

 its having been now 96 hours in a chamber, with a fire in it, by which it might 

 be wanned. This float a being taken out of the water, wiped, and laid in a dry 

 place for 24 hours, weighed 211 grains, having gained by absorption 21 grains 

 of additional weight. 



Exper. 4. The float, in this state, having been 24 hours out of the fresh 

 water, was now put into salt water brought from the North Foreland, in which 

 it was found to support the weight of 954 grains, of a leaden medallion, having 

 the power of buoying up 38 grains more in the sea water, than it did in the 



