1 3 ° 
Mr. Williams's additional Observations 
the old pots was found to be at 84 degrees, and that in the 
new, or porous ones, at 68. After remaining in that situa- 
tion one hour longer, the water in the old pots rose to 88 
degrees, whilst that in the new ones continued at 68. 
May 1st, at two o'clock in the afternoon, the thermo- 
meter then being, in the sun, at 110 degrees, and in the 
shade at 100, the experiment was repeated, with the same 
pots as before. After being filled with well-water, they were 
exposed for four hours, viz. from two o'clock till six, to a hot 
wind ; the water in the old pots was then found to be at 
97 degrees, that in the new ones at 68. 
The foregoing observations on the frigorific effect of eva- 
poration from porous vessels, will perhaps account, in some 
measure, for ice being formed when the thermometer, in the 
air, is above the freezing point. And the power of evapora- 
tion in generating cold, may be further elucidated by the fol- 
lowing observations on the effects produced, by its means, in 
our houses. 
May 16, 1792, at two in the afternoon. 
The thermometer, in the sun, with a hot westerly wind, 
rose to - - - -118 degrees. 
Ditto, in the shade, but exposed to the hot 
wind - - - 110 ditto. 
Ditto, in the house, which was kept cool by . 
tatties - - - - 87 ditto. 
June 7. 
Thermometer, in the sun 
Ditto, in the shade, and hot wind 
Ditto, in the house, cooled by tatties 
1 13 degrees. 
104 ditto. 
83 ditto. 
