1 6a EXPERIMENTS and OB SE R VA 27 ONS 



board immediately before I firft fet them out ; and after they 

 had remained abroad from forty-five minutes pad nine till near 

 two o'clock in the morning, they were again weighed, when 

 the fand had gained four-tenths of an ounce, and the fnow 

 very nearly three-tenths. 



A LITTLE after midnight, a thin circular board, which had 

 been previoufly cooled, was put over the fand, and fupported 

 at the diftance of about an inch and a half above the furface. 

 After feventeen minutes, it was removed, when the thermome- 

 ter on the fand pointed lower than the one in air by only two 

 degrees ; and probably, for the greateft part of this interval, 

 the cooling procefs had abated. 



IN a letter with which I had been favoured this day from Dr 

 BLACK, by whofe correfpondence upon this fubjecl; I think 

 myfelf highly honoured and obliged, there was fuggefted an 

 experiment with gauze to be laid over the thermometer, which 

 was accordingly tried. For this purpofe, I fattened with pack- 

 thread a piece of open gauze to a hoop of eight inches diameter 

 and an inch deep ; and, when the thermometers were fheltered 

 in this manner, the quickfilver commonly rofe nearly two 

 degrees. 



JANUARY 26. 1784. 



HAVING now found, that the fand was more efficacious than 

 the fnow in promoting this fingular kind of refrigeration, I 

 this night repeated the lafl experiment with fine powder of 

 wood charcoal, the loofe fhavings of brafs gathered from a 

 turner's lath, a friable amalgam of quickfilver and tin, the 

 fand and the fnow, to fee if there would be any remarkable 

 difference in the cold produced by fubflances differing fo much 

 in their nature and denfity. The apparatus confifled of circu- 

 lar boards, two feet in diameter, which I ranged in order upon 

 a long flender frame, fet at right angles to the direction of any 

 air that was {lining. I then covered them with the various 



materials 



