Xclv GENERAL RESULTS OF THE MAKERSTOUN OBSERVATIONS. 
TaBLE 87.—Diurnal Variation of the Atmospheric Pressure for each Astronomical Season and 
for the Year, deduced from the observations of the Years 1843-6. 
| 
Nov. | Feb. | 
Dee. | March. 
Jan. April. 
3 
8 
@ 
| 
in. | in. 
-0026 | + -0040 | 
0041 —-0013 
-0055 | —-0057 
-0108 |—-0112 
-0159 |—-0135 | 
0179 | —-0122 
—-0158 —-0092 
-0096  —-0043 | 
0012 +-0008 
.0060 +-0036 
0122 +-0059 | 
0098 +-0075 
FOOnMDNaAuRhWNre Oo: 
—— 
Table 87 has been formed thus :—The hourly means for each quarter were obtained for each year ; those for 
1844 and 1845 were corrected for continuous barometric change as described in the volume for 1844, p. 422, 
excepting that the change of pressure from 11 to 125, was considered equal to the mean of the changes from 
10" to 11" and from 12 to 14, (instead of from 10% to 11" only): the hourly means for each quarter were 
then combined in the manner already described for the magnetic declination, No. 26. 
TABLE 88.—Daily Epochs of Maximum and Minimum Atmospheric Pressure, with the Intervals 
from Epoch to Epoch, for each Quarter, and for the Year. 
Interval Interval ears Interval |! Mean Epoch betwixt 
Minimum G Maximum % Minimum Min Maximum the Two 
A.M. F A.M. . M. se P.M. 
Max. 
Period. 
Maxima. | Minima. 
Dec. Jan. 
Mar. Apr. | 
June July | 
Sept. Oct. | 
Year 
196. Diurnal Variation of the Atmospheric Pressure—From Table 87, this consists of two maxima and 
two minima in each quarter of the year: the approximate epochs in apparent time, as deduced from the projec- 
tions of Table 87 (see Plate IX.), are given in Table 88. 
lst, The principal maximum occurs in the evening in spring, and in the forenoon in the other quarters ; 
the principal minimum occurs in the morning in winter and spring, and in the afternoon in summer and 
autumn. 
2d, The morning minimum occurs earliest in summer and latest in winter, obeying something like the law 
of sunrise, though the difference of epochs is variable, the minimum occurring about 3 hours before sunrise in 
winter, and immediately before sunrise in summer: the epoch of minimum temperature had a nearly similar 
relation to that of sunrise, but the similarity of the relations of the two classes of facts is more apparent than 
real, since the temperature of the air varies little in winter from 6% p.m. till 8) a.m. 
3d, The morning maximum occurs latest in spring and earliest in summer, the difference of the epochs 
for the two seasons being nearly three hours, 
