594 - Afr. cavallo’s 'fherniometrical 
The above irifinrinnecl o-r-.^mlhr ir?r 1 n^Arl 
me to try the effe£t of the light of the Sun and of a lamp 
upon thermometers whofe balls were painted with dif- 
ferent colours. Dr. franklin’s experiment with the 
pieces of cloth fet upon fnow that was expofed to the 
Sun is very ■well known. The doctor found, that thofe 
pieces of cloth, whofe colour was darker, funk deeper in 
the fnow than the others, by which it appears, that they 
became hotter. My view was to examine thofe different 
degrees of heat imbibed by different coloured fubftances 
with precifion, in order to obferve if they kept any pro- 
portion to the fpaces occupied by the prifmatic colours in 
the prifmatic Spectrum, or if they followed any other dis- 
coverable law; but thofe attempts met with many diffi- 
culties, the greateft of which was the choice of colours. 
The water colours that are commonly ufed, as carmine, 
fap-green, See. are of fo different a nature from one ano- 
ther, that when the balls of the thermometers were 
painted with them, their furfaces were not equally 
fmooth, which occafioned great difference in the effect ; 
for I found, that two thermometers, whofe balls had 
been painted with the fame colour, but the paint laid 
fmoother on one than on the other, fhewed different 
degrees of heat when they were both expofed to the 
rays of the Sun. 
I attempted 
