LIPRAR* 
NEV, 
GOT A 
GAR 
ON THE 
REDUCTION OF THE BAROMETER 
TO SHA LEVEL. 
BY CHARLES CARPMAEL, M.A., F.R.A.S., 
(LATE FELLOW OF ST. JOHN’S COLL., CAMB.) 
Deputy Superintendent of the Meteorological Service of Canada. 
The application of an approximately correct reduction to baro- 
metric readings, taken at various levels, in order to reduce them to 
what they would have been at one specified level, is absolutely 
necessary for their intercomparison. In the following paper several 
formule which have been employed for this purpose are examined ; 
and tables are appended by means of which, with very little calcu- 
lation, a sufficiently correct reduction may be obtained, and which 
are, moreover, peculiarly adapted to the computation of tables of 
reduction for individual stations. 
Guyot’s Tables* D, XVI. and XIX”, are commonly employed, on 
this continent, for the purpose of effecting the reduction. These give 
the height, in English feet, of a column of air corresponding to a tenth 
> of an inch in the barometer at various temperatures, the barometric 
pressure at the base of the column being from 22 inches to 30-4 
inches. 
& A formula is given for use with Table XVI., which may be 
— 
ee 
written 
a 
W * 106’ 
* . where & represents the required reduction in inches, Z the differ- 
<2 ence of height between the two stations, or the height above the sea 
=» (expressed in feet), V the number in the table, # the observed reading 
of the barometer reduced to 32° Fahr., and } the pressure on which 
the tabular number JW is based,t that is, 30 inches. 
fit (i.) 
* Meteorological and Physical Tables. Third edition. Washington, 1859. By Arnold Guyot, 
P.D., LL.D., Professor of Geology and Physical Geography, College of New Jersey. 
+Guyot defines what is here represented by 0, as ‘‘the normal height of barometer at the sea- 
level,” and in an example which he gives, he employs 30 in. It is, however, only because the 
table is based on a barometric reading of 30 in,, that this value of } is to be employed. 
(Proceed. Can. Inst. Vol. I. Part #4.) 
