H. A. Hazen—Projection of Lines of Equal Pressure. 365 
Tables have been prepared on this system for Mt. Wash- 
ington, N. H., reducing to sea-level by comparison with Port- 
land, Me., also for nearly all the stations of the Signal Service, 
above 1000’ in hight, west of the Mississippi River; column 
6, Table I, is taken from such a table. For elevations under 
3000’ the U. 8. Signal Service have adopted a formula of reduc- 
tion which always gives results too small. 
n referring to Table I, we see that during the month of 
January, 1879, in one instance the reduction in column 4 was 
0-49 less than in column 6, and in two eases the reductions in 
column 4 were 0/50 less than in column 5. 
In the Annual Report of the Chief Signal Officer for 1876, 
are published tables computed by Lieut. Dunwoody, for reduc- 
Ing pressures at an elevation not exceeding 7000’ to sea-level. 
Table IV gives a comparison of reductions by these tables with 
those by Guyot’s tables and also Baily’s. 
TABLE LY. 
Reduction of Mt. Washington to sea-level. 
hb rcereae ee Ce 
| BS 5m Baily. Guyot. Dunwoody. Hazen. 
ibet. W.& P. 
Mean annual pressure 
Mt. W., 23-626 
Mean annual temp’ature s 
Mt. 36°93 6-356 6"316 6-342 6-314 6"°356 
Pressure Mt. W., 23"-00 
W. & Portland, 20° eG Oe 
Mean temperature Mt. 
W. & Portland, — 20° wade YUM fe ae 
Pressure Mt. W., 24”-00 
ean temperature Mt. 
W. & Portland, 60° 6-060 hey aoe ce 
Mean temperature Mt. 
W. & Portland, 20° 6685 OG! | Oe ee 
In column 1 are given pressures on Mt. Washington and the 
mean temperature between Mt. Washington and Portland. In 
_ the remaining columns are found the reductions to sea-level, as 
computed from various formule and tables 
Baily’s formula in column 3 has been 
Carpmael, Superintendent of the Meteorological Service of 
Canada, who regards the tables of Dunwoody as unsatisfactory. 
Tt would secm that all the results are nearly correct when 
the formule in different portions of its range giving the i 
results. On the whole the reductions by Guyot seem the bes 
