Peessure of Aqueous Vapour. 



Ixxxvii 



3d, The intervals between the epochs of mean temperature and of the maximum temperature are nearly equal 

 in spring and autumn ; the afternoon interval is greatest in summer, and it is least in winter. If we except 

 summer, the temperature increases as rapidly from the mean to the maximum, as it diminishes from the 

 maximum to the mean ; the slight difference in autumn between the values of the intervals, and even that in 

 summer may be due to error in the epoch of maximum resulting from the fewness of the observations. In 

 each quarter, with the exception of summer, the temperature diminishes more rapidly after the maximum till 

 sunset than it increased during equal time before the maximum.* It will be seen from the column for the year, 

 in Table 75, that the mean temperature for the pairs of hours before and after l^* and 2'* p.m., are equal or 

 nearly equal till the pair 9^ 10™ a.m. and 6^ 10™ p.m., which are also nearly equal, so that the mean diurnal 

 curve for the year from 9*^ 10™ a.m. till 6^ 10™ p.m. is symmetrical about a vertical axis. 



Pressure of Aqueous Vapour. 

 Table 77. — Mean Pressure of Aqueous Vapour for each Month in the Years 1843-6. 



Year. 



Jan. 



Feb. 



March. 



April. 



Slay. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



Mean. 





in. 



in. 



in. 



in. 



in. 



in. 



in. 



in. 



in. 



in. 



in. 



in. 



in. 



1843 



0-220 



0-184 



0-223 



0-253 



0^281 



0-320 



0^387 



0^409 



0-382 



0^245 



0-238 



0^280 



0^283 



1844 



•216 



•180 



•209 



•258 



•273 



•354 



•367 



•355 



-351 



•276 



•258 



•187 



•274 



1845 



•203 



•181 



•185 



■251 



•276 



•374 



•358 



-366 



-317 



•297 



•252 



• 207 



•272 



1846 



•251 



•249 



•222 



•254 



•298 



•409 



•425 



-443 



•397 



•306 



•269 



• 187 



-.309 



Mean 



•222 



•198 



•210 



•254 



•282 



•364 



•384 



•393 



•362 



•281 



•254 



•215 



•285 



183. Annual Variation of the Pressure of Aqueous Vajyour. — The pressure of aqueous vapour, as deduced 

 from the observations of the dry and wet bulb thermometers, is least in February, being in the mean of 4 years 

 = 0-198 inch of mercury, and it is greatest in August = b'393 inch, the difference between the greatest and least 

 monthly means being nearly two-tenths of an inch. The mean pressure for each of the four months December 

 to March varies little ; so also for the four months June to September. 



The mean pressure for the four months December to March from 4 years' observations = 0"211 inch. 



June to September = 0-381 ••• 



The mean pressure of aqueous vapour for the 4 years 1843-6 = 0285 ••• 



Table 78.- 



-Variations of the Pressure of Aqueous Vapour with reference to the Moon's Age and 

 Declination for the Years 1843-6. 















After 













Moon's 

 Age. 



1843. 



1844. 



1845. 



1846. 



Mean. 



Moon 

 farthest 

 North. 



1843. 



1844. 



1845. 



1846. 



Mean. 



d. d. 



in. 



in. 



in. 



in. 



in. 



d. d. 



in. 



in. 



in. 



in. 



in. 



14—16 



•000 



-t--004 



-i--007 



+ -012 



+ •006 



27— 1 



-•030 



--001 



-•017 



-■001 



-•012 



17—20 



-J- .008 



+ -011 



--005 



+ •002 



+ •004 



2— 5 



-•003 



-•002 



+ •001 



-•020 



-•006 



21—24 



+ •009 



-f-015 



-•021 



-Oil 



-•002 



6— 8 



-•022 



-•010 



+ •017 



+ •002 



-•003 



25—28 



-•001 



--005 



-F-OlO 



+ -003 



+ -002 



9—12 



+ ■016 



+ •001 



+ •007 



+ •003 



+ •007 



29— 1 



-•003 



--013 



+ •007 



+ -002 



--002 



13—15 



+ •002 



+ -007 



-•003 



+ •001 



+ •002 



2— 5 



-•020 



--004 



-•010 



--008 



--010 



16—19 



+ •017 



--006 



-004 



+ ■008 



+ •004 



6— 9 



-i--006 



-t--008 



+ •007 



+ ■002 



+ -006 



20—22 



-■003 



+ -007 



■000 



+ ■006 



+ •002 



10—13 



--001 



-•017 



+ •008 



--005 



--004 



23—26 



+ -021 



+ •003 



-■004 



•000 



+ •005 



184. Variations of the Pressure of Aqueous Vapour with Reference to the Moon''s Age. — Though it has not 

 been possible to determine by our apparatus the heating effect of the moon, yet it is believed that it has some 



* The difference betwixt this result and that obtained by others is due, it is conceived, to the want of proper precautions to 

 avoid the effects of radiation or reflection of the sun's heat from the soil or surrounding objects in the afternoon. It will be seen, 

 in the Introductions to the several volumes, that this source of error was cared for at Makerstoun. 



MAG. AND MET. OBS. 1845 AND 1846. y 



