59° M>\ cavallo’s 'Thermometrical 
When thefe thermometers were expofed to the Sun, 
or kept in the fhade, they the wed the fame degree pre- 
cifely. The difference between the degree fhewn by 
thefe thermometers when expofed to the Sun, and when 
kept in the fhade at about the fame time of the day, was 
very trifling. 
When the ball of one of thofe thermometers, which 
we fhall call a, was painted black with Indian ink, or with 
the fmoke of a candle, and that of the other thermomer 
ter b was left clean, on being expofed to the Sun they 
fhewed different degrees of temperature ; the quickfilver 
in the tube of A was much above the quickfilver in the 
tube of b. This difference fometimes amounted to about 
io°. but it was never conftant, varying according to the 
clearnefs of the Sun’s light as well as of the air, and alfo 
according to the different degrees of temperature of the 
atmofphere. 
Keeping the frame with thofe thermometers, one of 
which had the ball painted black, hung on the fide of 
a window, I obferved a remarkable fa<5t, viz . that thefe 
thermometers fhewed unequal degrees of heat, not only 
when prefented to the Sun, but alfo when expofed to the 
ftrong day-light. I cleaned the bulb of the thermome- 
ter a, and blackened that of b, but the effeft was con- 
ftant, viz. the quickfilver in the tube of the thermometer, 
whofe. 
