Experiments and Qbfervations. 591 
'whofe bulb was painted black, was conftantly higher 
than the other, whenever they were expofed to the 
ftrong day-light. This difference was commonly about 
one-third of a degree, but fometimes it amounted to 
three-fourths, and even to a whole degree. The fituation 
in which thofe thermometers were ufually placed was 
fuch.that the light of the Sun could not be reflected upon 
them by any objedt ftanding before; but the experiment 
anfwered even when the Sun was hidden by clouds. 
This obfervation feemed to fhew that, perhaps, every 
degree of light is attended with a proportionate degree 
of heat; and induced me to try, in a fxmilar manner, 
whether, by directing the concentrated light of the Moon 
upon the blackened ball of one of thefe thermometers, I 
could render fenlible the. effedt of that light (a) . But al- 
though I attempted it fome time ago with a large lens 
feveral times, and have lately tried it again with a burn- 
ing mirror of eighteen inches diameter, yet fometimes 
for want of proper means of obferving the height 
of the mercury in the tubes of the thermometers, fome- 
times for want of a continued clear light of the Moon, 
and in fhort from one unfavourable circumftance or 
(a) The concentrated light of the Moon has often been thrown upon ther- 
mometers without any efFtdt; but I do not know that any blackened thermo- 
meter was ever ufed before for this purpofe. 
other, 
