588 Mr. cavallo’s Thermometrica l 
Having read in a volume of the Philofophical T«nf 
actions the account ot an experiment made with a ther- 
mometer, whofe bulb was painted black, and was expofed 
to the rays of the Sun, in which cafe it had been found, 
that the thermometer fhewed a much greater degree of 
heat than when not blackened, I was defirous of trying 
the ultimate limits of this difference. For which purpofe 
I eonftrufled two thermometers, the fcales of which 
(being made by, trial) coincided fo perfectly well together, 
that when the thermometers were put in equal circu rn- 
ftances, ho difference could be perceived between the de- 
grees of heat (hewn by them. The method ufed to gra- 
duate thofe thermometers is as follows. The fcale of 
one of the thermometers was made in the ufnal manner, 
viz, by finding the boiling and freezing water points, 
and dividing that diftance into 186 equal parts, which 
are the degrees according to Fahrenheit. Here no 
regard was paid to the barometrical height at the time of 
finding the boiling, water point, it being ufelefs for the 
experiment for which the inftrument was intended. This 
done, the balls of the two thermometers were put into hot 
water, and according as the water cooled, and confequently 
the mercury defcended in the tubes, different marks were 
put upon, the tube of the ungraduated thermometer, 
6 which 
