366 HH. A. Hazen— Projection of Lines of Equal Pressure. 
and those by Dunwoody are next. These discrepancies are 
still greater in the case of reductions of pressures at such an 
altitude as Pike’s Peak. This is shown clearly in Table V. 
TABLE V. 
Reduction of Pike’s Peak to sea-level. 
Guyot. Hazen. 
Tempera- 
ture. a “raga 
By is by lar ay". 176: FY Gisbes 17''8. 
60° TE'6) 11"°67 i ey 11°94 11"-93 117-92 
50 11°92 LE 39 12°06 12:11 12°10 12:09 
40 12°26 E2733 12°40 12°27 12°26 12°25 
30 12°62 12°69 12°76 12°43 12°42 12°41 
20 13°00 13°07 13°i4 12°59 12°58 12°57 
10 13°38 13°46 13°54 12°76 12°45 12°74 
0 13°81 13°89 13°97 12°93 12°92 12°91 
There seems to be a variation by these two methods of re- 
duction of nearly one inch at 0° temperature. it be objected 
that no account is taken of pressures at the lower station, an 
that comparisons made between stations 300 miles apart would 
differ from those near each other, also that the altitude of 
Pike’s Peak is uncertain. It may be said that the extreme 
e most marked peculiarity in the two tables, however, 1s 
that while the reduction by Guyot increases with an tncrease © 
pressure, the actual reduction diminishes. This fact has been 
verified by reductions at a large number of stations. : 
The method proposed then consists in this. All reductions 
of pressures at altitudes not exceeding 1000’ be made by the 
use of Guyot’s formula. (Table VI, for facilitating this redue- 
tion is appended to this paper.) For all other stations reductions 
be made from tables specially prepared, from a comparison of 
observations at an elevated and at a lower neighboring station. 
Plates are given, showing a projection of isobars over the 
whole of the United States, for the observation at 7.85 A. M. 
Washington time, from the 2d to the 7th of February, 1880. In 
making these reductions, the actual temperature at the station 
has been used for all except Pike’s Peak, at the latter station 
the mean temperature between Pike’s Peak and Dodge City has 
been employed. ‘The isobars have been projected from the re- 
ductions at ai/ the stations except Pike’s Peak, Salt Lake City, 
Deadwood, Fort Buford and Fort Stevenson. Observations have 
not been published to a sufficient extent to give satisfactory 
tables for reduction in the last three cases ; at Salt Lake City the 
temperatures are troublesome, and Pike’s Peak is very high. 
