Monthly Vaeiations for the Atmospheric Pressure. 
xciii 
The monthly mean diurnal range does not vary greatly in the six months for which tlie svm is sonth of 
the equator, nor in the six months for which it is north of the equator ; thus, the mean range for the six 
months October to Mai-ch = 0-257 in., and for the six months April to September = 0-170 in. On the 
whole, the diurnal range varies inversely -with the monthly mean pressure. See No. 197 where the i-anges of 
the mean diurnal variations are considered. 
Table 86. — ^Variations of the Diurnal Range of Atmospheric Pressure, with reference to the 
Moon's Age and Declination for the Years 1843-6. 
Moon's 
Age. 
1843. 
1844. 
1845. 
1846. 
Mean. 
After 
Moon 
farthest 
North. 
1843. 
1844. 
1845. 
1846. 
i Mean. 
d. d. 
in. 
in. 
in. 
in. 
in. 
d. d. 
in. 
in. 
in. 
in. 
14—16 
+ •012 
-•032 
-•063 
-•027 
-•027 
27— 1 
+ •031 
+ •019 
+ •026 
+ •022 
+ -obs 
17—20 
-•014 
•000 
+ •049 
•000 
+ •009 
2— 5 
+ •010 
+ •022 
-•006 
+ •004 
+ •008 
21—24 
-•034 
+ •017 
+ •069 
+ •030 
+ •021 
6— 8 
-•001 
+ •009 
-•005 
-•053 
-•012 
25—28 
+ •001 
-•001 
-•009 
-•003 
- -003 
9—12 
+ ■010 
-•018 
-•021 
+ •010 
-•005 
29— 1 
+ •030 
+ •024 
+ •005 
+ •005 
+ •016 
13—15 
-•032 
-•026 
+ •019 
+ •009 
- ^008 
2— 5 
+ •010 
+ •0)1 
+ •002 
+ •019 
+ •011 
16—19 
-•028 
-•007 
-•003 
-•002 
'-•010 
6— 9 
+ •001 
+ •026 
-•Oil 
+ •008 
+ •008 
20—22 
+ •015 
- -Qlb 
-•033 
-•005 
'-•010 
10—13 
-•007 
-•044 
-•045 
-•033 
-•032 
23—26 
-•003 
+ •016 
+ ■026 
+ •019 
+ •015 
194. Variation of the Diurnal Range of Atmospheric Pressure with the Jlooa's Age. — Investigations have 
been entered into by different meteorologists for the purpose of exhibiting the effect of the varying position of the 
moon upon the mean daily pressui'e of the atmosphere ; their success has been on the whole very doubtful. In 
our latitudes it is not easy to extricate the laws of these variations on account of the magnitude of the irregular 
changes ; it was for this reason that, after discussing the daily mean pressures for the year 1843 with refer- 
ence to the lunar arguments, the discussion of the diurnal ranges was substituted for that of the daily means ; 
as it was conceived that the variation of the diurnal range might be considerable (as in the case of the oceanic 
tides, &c.), though the variation of the mean should be nearly or altogether zero ; such had been found to be 
the case for the magnetic declination. The results of these discussions for each year, and for the mean of four 
years, are given in the first part of Table 86. The results for the four years are wonderfully consistent, and 
that of the mean of the four years may be expressed thus. — The diurnal range of the barometer is a minimum 
near opposition, and it is a maximum about the beginning of the second quarter, and immediately after con- 
junction ; perhaps the intermediate minimum near conjunction is accidental and might disappear in a larger series. 
The range of these mean numbers is very considerable, upwards of half-a-tenth of an inch, and it is probable 
that had the means for single days of the argument been given, the i-ange would have been nearly twice as 
great. This result is wholly different from what we should have expected when comparing the oscillation of 
the atmosphere with that of the ocean, and it appears diflicult to offer an explanation for it ; we shall find how- 
ever when we examine Table 91, that it is probably connected M ith the force of the wind ; at least that obeys 
the same law, the diurnal range of the barometer being greatest when the force of the wind is greatest. 
195. Variation of the Diurnal Range of the Atmospheric Pressure with Reference to the Moon^s Declina-' 
tioii. — The values for four years for this argument are given in the second part of Table 86 ; the results for 
each year agree here also to a remarkable extent with that shewn by the mean of the whole four years. The 
diurnal range of the barometer is a maximum when the moon is farthest north, it is a minimum when the 
moon is south of the equator. This result is also connected with that for the force of the wind (see No. 201), 
the diurnal range of the barometer being greatest when the force of the wind is greatest, and vice versa. 
