J. Lewis on the Barometer. 235 
The question of compensation will now be examined, requir- 
ing only the comprehension and aid of the artisan that it may be 
___ wrought into a practical solution, at once available for the pur- 
___ poses of the meteorologist. 
e i \ 
which (involved in the square of the diameter) tend to diminish 
the elevation of the mercury by enlarging its sectional area, so 
: 
_ that the elevation of the column might be expressed by 3825,, 
referring to a tube closed at its base and open at top; the excess ae 
oo. original elevation may be expressed by the terms 
82(;5—1). This last expression is less than the unit of excess 
of elevation due to temperature =82(A—1) which it is neces- 
‘ary should be attained in the long arm of the syphon, to estab- 
compensation, (presuming that it is attainable as a theoretical 
sage 
82(j 
elevation may be obtained from the expression 32(A—1 
_ © The minimum di wuld not be Jess than half an inch; the maximum di- 
ameter, on the other Side exceed one inch. A compromise between cos 
muy suggest something between these extremes. 2 
