[ 78 ] 
ments, the ratio of its decreafe were found regular 
in proportion to the diftance from the earth, its height 
might be eflimated with a much greater degree of 
precifion than it has been hitherto ; though it feems 
generally allowed that its real height cannot poffibly 
be afcertained. 
The impoffibility of obferving the difference of the 
preffure of the atmofphere at fmall diftances with 
accuracy by a common barometer, the fcale of which 
is but 3 inches, is very evident ; how far this inflru- 
ment, the fcale of which is 90 inches, might be con- 
ducive to the purpofe, is fubmitted to the judgment 
of others. 
I fhould imagine it would not be difficult, with a 
proper teakle, to raife a barometer of this kind gently, 
as high as 200 feet; and if it were raifed from the 
ground, and let down again from each diftance of 
20 feet, the regifters would mark very exadtly to the 
600 part of an inch at what height the mercury flood 
at each diftance ; fo that the weight of each column 
of aip of 20 feet, to the height it could be raifed, 
would be found pretty exactly. And if a proper 
apparatus were fixed for railing the barometer, the 
experiments might be repeated, as often as requilite, 
with very little trouble. 
Experiments of this nature cannot well be made 
by a Angle perfon ; but if an inffrument of the kind 
fhould be deemed ufeful for the purpofe, I fhould 
very willingly lend it, and alfo any affiftance I could 
give, in making the experiments. 
I fhall with great pleafure fhew you the inftru- 
ment whenever you favour me with your company; 
or 
