390 Of the Propagatio7t 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 ^^ of an inch in thickness ; and the other ^-| 

 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, about f of an inch in depth, 

 having by accident been left standing in an open glass 

 J£(r, 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 



