760 Col. roy’s Experiments for 
fures that fhould, in my opinion, be taken to bring the 
theory of the barometer to a ftill greater degree of per- 
fection, fuch as I believe it to be really capable of. 
By infpeCtion of the tables containing the computa- 
tions of the Britifh obfervations, it will be fcen, that the 
error of the rule is in general very fmall. In the Lon- 
don clafs it is greateft on Shooter’s-liill, making the 
height five feet too little. In thofe at Tay bridge, one of 
the obfervations on Schihallien gives a defective refult of 
29^ feet; but this is eafily accounted for, as it certainly 
arofe from the fhort time given to the barometer to lofe 
the heat it had acquired in carrying upwards, thofe 
deftined to obferve at the fummit arriving there too late, 
that is to fay, towards the expiration of the whole hour 
which the inferior barometer had been obferved in. One 
of the obfervations on Carmichael-hill, though a fmall 
height, is defective eight feet, which I afcribe to the 
South-weft wind and humidity of the air. From the 
fame caufe I would account for the uniform defeCt in 
, the firft part of the Edinburgh obfervations : in the laft 
part of thefe, the circumftances having changed, the er- 
ror hath the contrary fign. In the Linhoufe clafs ol ob- 
fervations, the fame caufe of defeCt appears on the ift 
of December, 1775, an( f on t ^ ie 20th of November, 
and 1 7th of December, 1776. The only refult which I 
confider 
