an Experiment on Heat. 3 r 5 
• The apparatus with the paffeboard diaphragm was expofed 
flill to the fun ; that with the iron was removed, and buffered 
to cool till its thermometer (hewed 107°; it was then expofed 
again to the fun till it had acquired the heat of 1 io°, to which 
degree the apparatus with the paffeboard hardly reached. The 
windows were now fhut. The heat of the room had arifen to 
8o°. Both the apparatus’s were placed on a table ; the doors were 
fhut, lo that there was no current of air. 
Paffeboard apparatus, after 30 minutes. Iron apparatus. 
96 104 
Aft^r 75 minutes, or 1 h. 45' from the beginning. 
83 89 
After 2 h. or 3 h. 45' from removal from the fun. 
78 room 75 80 
A fimilar refult arofe when there were no glaffes to exclude 
the external air. Likewife when the diaphragms were changed 
from one apparatus to the other. 
If any one wifhes to repeat thefe experiments, he muff take 
care that the fize of both apparatus’s be the fame ; the weight 
the fame, excepting the difference of the iron and paffeboard ; 
that they be equally fluffed, and perfectly dry : for if there be 
the lead moifture, the evaporation will not only make a fallacy 
in the experiment, but it will foon oblcure the glafies, fo as to 
prevent the rays of the fun from pafling through them. 
The firft thing to be noted in this experiment is, that the 
rays of the fun a&ed on the fame black paint only : for it was 
fo thick, that the rays could not penetrate to the iron or paffe- 
board below. The colour was the fame, and there was the 
fame glofs ; if any thing, that on the iron, in the experiment 
related, was rather more gloffy, in order that it might not be 
favoured^. 
