390 Of the Propagation of Heat 



On repeating this experiment, and varying it by using 

 a cake of fine bleached bees-wax^ instead of tallow, the 

 result was much the same ; the protuberance, however, 

 in the middle of the circular cavity occupied by the 

 melted wax, though perfectly perceptible, was less con- 

 siderable in height than that in the cake of tallow. 



4- Beautiful Crystals of Sea-Salt formed in Brine standing 



on Mercury. 



A small quantity of strong brine, standing on mer- 

 cury in an open glass tumbler, having by accident been 

 left in a room in a retired part of the house, I observed 

 at the end of about six months that two beautiful crys- 

 tals of salt, perfectly quadrangular, had been formed in 

 it, one of which was \ of an inch long, \^ of an inch 

 wide, and -fa of an inch in thickness ; and the other ^f 

 of an inch long, \^ of an inch wide, and -^ of an inch 

 thick. 



Did the Fluid mercury on which this brine reposed 

 contribute and how to the regularity of the form 

 and the uncommon size of these crystals? And might 

 not beautiful crystals of other salts be procured by simi- 

 lar means ? 



5. Olive-Oil rendered colourless by Exposure to the Air 

 standing on Brine. 



A quantity of olive-oil y about f of an inch in depth, 

 having by accident been left standing in an open glass 

 jar, about four inches in diameter, on about a quart of 

 brine, moderately strong, in a retired room where the 

 sun's rays never enter, at the end of about six months I 



