Ixxxviii 
Geneeal Results of the Makeestoun Obseevations. 
effect, especially on the aqueous contents of our atmospliere ; in order if possible to detennine this, the discus- 
sions, of which the results are contained in Table 78, were made for each year; the means of the 4 years 
indicate as follows, — • 
1st, That on the whole, the pressure of aqueous vapour was greater about opposition than about conjunc- 
tion ; the average pressure of each of the 15 days forming the second and third quarters being 0-003 inch 
above the mean, and of each of the 15 days forming the fourth and first quarters being 0-003 inch below the 
mean. 
2d, That the pressure of aqueous vapour was greatest from about the period of the moon''s farthest 
southerly position, till near its farthest northerly position ; that it was least from its farthest northerly position 
till it was nearly farthest south. 
Sd, If the first result be considered true, then the aqueous vapour pressure varies with the moonlight ; as 
this pressure is greatest in the months from June to September (No. 183), during which the moon is in con- 
junction in its ascent from its most southerly declination, and least in the months from December to March, 
during which it is in conjunction in its descent from its most northerly position, the second result is probably 
a consequence of the first. 
Table 79. — Diurnal Variation of the Pressure of Aqueous Vapour for each Astronomical Season 
and for the Year, deduced from the Observations of the Years 1843-6. 
Mak. 
Mean 
Time. 
Nov. 
Dec. 
Jan. 
Feb. 
March. 
April. 
May. 
June. 
July. 
Aug. 
Sept. 
Oct. 
Year. 
Mak. 
Mean 
Time. 
Nov. 
Dec. 
Jan. 
Feb. 
March. 
April. 
May. 
June. 
July. 
Aug. 
Sept. 
Oct. 
Tear. 
li. m. 
in. 
in. 
in. 
in. 
in. 
li. m. 
in. 
in. 
in. 
in. 
in. 
12 10 
-0-005 
-0-007 
-0-013 
-0-015 
0-010 
0 10 
+ 
0^011 
+ 
0-012 
+ 
0-015 
+ 0^024 
+ 
0-015 
13 10 
- -005 
- -009 
- -016 
- -018 
•012 
1 10 
+ 
•013 
+ 
•Oil 
+ 
•015 
+ -024 
-1- 
-016 
14 10 
- -005 
- -010 
- -020 
- -024 
-015 
2 10 
+ 
•012 
+ 
•Oil 
+ 
•016 
+ ^023 : 
+ 
•015 
15 10 
- -005 
- -012 
- -024 
- -025 
-017 
3 10 
+ 
•009 
+ 
•008 
+ 
•013 
+ ^021 
-t- 
•013 
16 10 
- -005 
- -014 
- -024 
- -028 
-018 
4 10 
+ 
•005 
+ 
•007 
+ 
•012 
+ •oig 
-1- 
•Oil 
17 10 
- -005 
- -012 
- -017 
- -030 
•016 
5 10 
+ 
•002 
+ 
•006 
+ 
•013 
+ -017 
+ 
-009 
18 10 
- -004 
- -010 
- -005 
- -024 
-Oil 
6 10 
•001 
+ 
•002 
+ 
•009 
+ •014; 
+ 
-006 
19 10 
- -005 
- -005 
+ -001 
- -Oil 
•005 
7 10 
•002 
+ 
•001 
+ 
•008 
+ -010' 
4- 
•004 
20 10 
- -004 
-000 
+ -006 
+ -003 
+ 
-001 
8 10 
•003 
•000 
+ 
•004 
+ -004 
+ 
-001 
21 10 
- -001 
+ -004 
+ -008 
+ -014 
+ 
•006 
9 10 
•003 
•003 
•002 
- -004 
•003 
22 10 
+ -004 
+ -007 
+ -010 
+ -019 
+ 
•010 
10 10 
•004 
•004 
•006 
- •OOQ 
•006 
23 10 
+ -008 
+ -010 
+ -012 
+ -022 
+ 
•013 
11 10 
•005 
■004 
•010 
- -015 
•008 
185. Diurnal Variation of the Pressure of Aqueous Vapour. — The following are the approximate epochs 
of the minimum and maximum, as deduced from Table 79. 
Winter, Nov., Dec, Jan., Minimum, 111^ p.m. — 7'^ a.m. Maximum, l** 30™ p.m. 
Spring, Feb., March, April, 4*' 10™ a.m. 0"^ 40"" p.m. 
Summer, May, June, July, 3*^ 50™ a.m. 30™ p.m. 
Autumn, Aug., Sept., Oct., 5'MO™ a.m. 0'' 40™ p.m. 
Year, 4'' 0™ a.m. 1'' 10™ p.m. 
These epochs do not differ greatly from those for the temperature of the air, the principal difference is to be 
found in the variation of the epochs of maximum with season ; the maximum pressiu'e of aqueous vapour 
occurs earliest near the equinoxes, and latest near the solstices, whereas the reverse is the case for the tem- 
])erature of tlie air. In the mean for the year, the mean pressure of aqueous vapour occurs at 8'' 0™ a.m., and 
at 8"' 25'" P.M., tlic interval being 12'' 25™. 
The range of the diurnal variation for the "Winter (juarter = 0-018 inch. 
Spring = 0-026 
Summer = 0-040 
Autumn = 0-054 
Year 
= 0 034 
