728 Col. roy’s Experiments for 
render the computations of them feparately wholly un- 
neceffary. 
Except in very fmall heights, and chiefly in London, 
where it was impoflible to fcreen the upper barometer fo 
effectually from the Sun during the time of obfervation 
as that below, which generally flood in the fhade of fome 
building, the temperature of the quickfilver in the fu- 
perior ll:J hath been colder than that in the inferior baro- 
meter. The difference was commonly found to be two 
or three degrees; fometimes it would amount to fix 
or feven; rarely, in heights that were confiderable, to 
nine or ten; and in one inflance only to thirteen, where 
the vertical diftance of the inftruments was great. 
Whether in the plain or on the tops of the higheft 
mountains, the detached thermometers, indicating the 
temperature of the air, have generally flood fomething 
( k) I have fometiaies found, particularly in -frofty. weather, that a thermo- 
meter placed on the pavement of the North-fide of St. Paul’s Church-yard, 
elofe to the wall of the. building, would Hand two degrees lower than that which! 
was expofed on the North-fide of the iron gallery over the dome. The firft, no 
doubt, felt the cold produced by the evaporation from the fiones, while that 
above might be affefted by the afcending fmoke. But the moft remarkable, 
balance °f this kind. occurs in one. of Dr-, lino’s obfervations, on the breaking 
up of the hard froft January 31, 1776: at Hawk-hill, at io h 45" A.M. the 
temperature of the open air was 14°, while that at the fummit of Arthur’s Seat 
was 20°. The frpft that remained in the ground kept the air extremely cold, 
below, though it had already felt the effefls of the thaw at the top of the 
mountain. 
lower 
