|xxxvili GENERAL RESULTS OF THE MAKERSTOUN OBSERVATIONS. 
effect, especially on the aqueous contents of our atmosphere ; in order if possible to determine this, the diseus- 
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. 
3d, 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. 
TasLE 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. 
KOCOOCONOQuURWNR OF 
b+++++4+44 
— 
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, Noy., Dec., Jan., Minimum, 11) p.m.—7" a.m. Maximum, 1 30™ p.m. 
Spring, Feb., March, April, 45 10™ a.m. 0» 40™ p.m, 
Summer, May, June, July, 35 50™ am. 1h 30™ p.m. 
Autumn, Aug., Sept., Oct., 5» 10™ a.m. Om 40™ p.m, 
Wearsi-o. Tinted] The ote kee AU. OVS a A 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 pressure of aqueous vapour 
occurs earliest near the equinoxes, and latest near the solstices, whereas the reverse is the case for the tem- 
perature of the air. In the mean for the year, the mean pressure of aqueous vapour occurs at 8" 0™ .m., and 
at 8" 25m p.m, the interval being 125 25™, 
The range of the diurnal variation for the Winter quarter = 0-018 inch. 
SPLS bs. ss = 0:026 
Summer ...... = 0:040 
Autumn ...... = 0:054 
Year = 0-034 
