meafurlng Heights •with the Barometer . 727 
made others of the cold kind, on the Cairn-hills in his 
neighbourhood. From the combination of the whole of 
thefe obfervations taken together, and a comparifon of 
them with Mr. de luc’s, as far as they are fimilar, I 
mean to drew the agreement or otherwife, between the 
equation for the heat of the air, as deduced from the ba- 
rometer and manometer; but lince the Britifli obferva- 
tions, in certain cafes, differ confiderably in their circum- 
ftances from thofe on Saleve, it is necefiary, in the firft 
place, to point out wherein this difference chiefly con- 
flfts. 
In the obfervations in Britain, the barometers and de- 
tached thermometers have been,almoft conftantly, placed 
in the open air in the fhade, and fuffered to remain there 
generally half an hour, and fometimes a great deal 
longer, before the correfponding obfervations were be- 
gun, that the quickfilver might have time to take the 
temperatures of the fituations refpedtively . They were 
then obferved four times, ufually at intervals of ten mi- 
nutes, the mean of the four being that which is calcu- 
lated, and called a Angle obfervation. If the time did not 
admit of fb long an interval, the fame number of obfer- 
vations were taken at diftances of five minutes from each 
other. In either cafe, the extremes never differed above 
a few thoufandth parts of an inch from the mean, fo as to 
Vol. LXVII. 5 A render 
