t i°3 ] 
VIII. Experiments on local Heat. In a Letter from James Six, 
Ej(j. to the Rev. Francis Wollafton, LL.B, F. R. S. 
Read January io, 1788. 
DEAR SIR, 
T HE following experiments are a continuation of thole 
I had the pleafure of communicating to you fome time 
fince, relating to the diverfity of local heat in the atmofphere ; 
and confirm, in a more particular manner, my former obfer* 
vations refpe£ling a remarkable refrigeration, which, in clear 
weather, takes place near the earth ; for, although its furface 
in the day-time is then moft liable to be heated by the fun, yet 
after that is fet, and during the night, the air is always found 
coldeft near the ground, particularly in vallies. This pheno- 
menon, for want of noflurnal obfervations, has been but lately 
noticed probably becaufe in the day-time, efpecial.ly when 
the 
* Within thefe few years. 
Mr. Wilson, in the Philofophical Tranfa&ions, 1780, p 467. and 1781, p. 
368. defcribing the eifeds of a Severe froft at GlaSgow, mentions a remarkable 
refrigeration, which he perceived to take place on the Surface of the Snow and. 
hoar-froft, which Sunk the mercury in a thermometer laid upon it many degrees 
lower than one SuSpended twenty four feet above it. This phenomenon,, he Says, 
had recently come under ohfervation . ; but SuppoSing (I preSume) the principle of 
refrigeration to operate only on the Surface of the Snow, or hoar-froft, when the 
cold was Severe, it doss not appear he made experiments at any other time. 
In 
