592, Mr. cavallo’s T’hermometrical 
other, I have not yet been able to make a fair and decifive 
trial of this experiment. 
The light of the Sun being very inconftant on account 
of clouds and of its diurnal motion, I thought to make 
fome experiments with the above mentioned two ther- 
mometers, by ex poling them to the light of a lamp, and 
I found that this light had a confiderable effect upon 
them. 
The ball of one of the thermometers being blackened, 
and both being fet at two inches diftance from the flame 
of a lamp, they both rofe from 5 8°, at which the mer- 
cury flood before the lighting of the lamp, to 65°^, and 
the blackened thermometer to 67°^. Another time, being 
fet at the fame diftance from the lamp, the uncoloured 
thermometer came up to 67°!, and the blackened one to 
68°|. In fhort, by various repeated trials it appeared, 
that the difference generally amounted to about i°. 
When the thermometers were put farther than two 
inches from the lamp, this difference decreafed, and at 
about fourteen or fifteen inches it vanifhed quite. 
It is mathematically true, that emanations which pro- 
ceed from a center, and expand in a fphere, mu ft conti- 
nually become more and more rare in proportion to the 
fquares of the diftances from the center. Thus it is faid, 
that the intenftty of light proceeding from a luminous 
body 
