'C 6 o Col. roy’s Experiments for 
_rate as well as maximum of expanfion was afcertained : 
• • 
wherefore thofe of the two preceding claffes need only 
be mentioned in a general way. 
The firft fet of the firft clafs comprehended fuch as 
were made with one barometer in a cold room, or in the 
open air, and the other in a room on the fame level with 
the former, where there was conftantly a fire, which was 
occafionally increased, in order to augment the difference 
of temperature. When the heated barometer had re- 
mained feveral hours in an angle of the room, the dif- 
ference of temperature of its quickfilver above that of 
the coldeft, as indicated by their refpedtive attached ther- 
mometers, rarely exceeded i o or 1 2°, which, from a 
mean of many obfervations, gave an expanfion of .0333 
decimals of an inch, for the 1 o° comprehended between 
32 and 42°of Fahrenheit’s thermometer. So far the re- 
fult ariling in this way, from fmall differences of tem- 
perature, will be found to agree with the third clafs of 
^experiments. 
But when, in the fecond fet of this firft clafs, the dif- 
ference of temperature was augmented to 20 or 30°, by 
expofing the barometer within doors to a greater heat,, 
or placing the fuperior one on the leads, whereby it re- 
ceived the direift and reflected rays of the Sun through- 
out the greateft part of the day, while the other was kept 
