Ixxxviii 



General Results of the Makeestoun Observations. 



effect, especially on tlie aqueous contents of our atmosphere ; in order if possible to determine 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 0003 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. 



3<i, 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. 



Nov. 



Feb. 



May. 



Aug. 







Mak. 



Nov. 



Feb. 



May. 



Aug. 







Mean 



Dec. 



March. 



June. 



Sept. 



Year. 



Mean 



Dec. 



March. 



June. 



Sept. 



Y 



ear. 



Time. 



Jan. 



April. 



July. 



Oct. 







Time. 



Jan. 



April. 



July. 



Oct. 







I). m. 



in. 



in. 



in. 



in. 





in. 



li. m. 



in. 



in. 



in. 



in. 



.n 1 



12 10 



-0005 



-0007 



-0-013 



-0-015 



- 



0-010 



10 



+ 0011 



+ 0012 



+ 0-015 



+ 0024 



+ 



•015 



13 10 



- -005 



- -009 



- -016 



- -018 



_ 



•012 



1 10 



+ 013 



+ •Oil 



+ -015 



+ ^024 



+ 



•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 



+ 



•013 



16 10 



- -005 



- 014 



- -024 



- -028 



- 



-018 



4 10 



+ ^005 



+ -007 i+ -012 



+ •oig 



+ 



•Oil 



17 10 



- -005 



- -012 



- -017 



- -030 



- 



-016 



5 10 



+ -002 



+ •ooe 



+ -013 



+ •017 



+ 



•009 



18 10 



- 004 



- -010 



- -005 



- -024 





-Oil 



6 10 



- •OOl 



+ ^002 



+ -009 



+ •OH 



+ 



•006 



19 10 



- -005 



- -005 



+ 001 



- Oil 





-005 



7 10 



- 002 



+ 001 



+ -008 



+ 010 



-1- 



•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 



- •ooe 



- 009 



— 



006 



23 10 



+ -008 



+ 010 



+ -012 



+ -022 



+ 



•013 



11 10 



- •OOS 



- 004 



- •OlO 



- ^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., 



Spring, Feb., March, April, 



Summer, May, June, July, 



Autumn, Aug., Sept., Oct., 



Year, 



^linimum. 



11'' P.M. 7'' A.M. 



4'' 10™ A.Ji. 



S^ 50™ A.M. 

 6^ 10™ A.M. 



4'' O™ A.M. 



Maximum, 



l*" 30™ P.M. 



Qh 40tn p M_ 



Ih 30™ P.M. 

 0^ 40™ P.M. 



P lO™ 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™ a.m., and 

 at 8'' 25™ P.M., the interval being 121* 25™. 



The range of the diurnal variation for the Winter quarter = 0-018 inch. 



Spring = 0-026 ... 



Summer =0040 ... 



Autumn = 0-054 ... 



Year 



= 0-034 



