AND PRESSURE OF VAPOUR. 



307 



(measured from left to right) to N b E, and that it falls with winds 

 from NNE to SW. The same rule also holds (within a point) in 

 summer and winter separately, and is true also with respect to the 

 changes in the pressure of dry air. The pressure of vapour increases 

 with a wind between E N E to SW b S and diminishes with a wind 

 between SW and NE. 



On the average of the year, and during the winter half-year, both 

 the rise and fall have an uninterrupted progression ; and the same is 

 true in every case where the change is an increase ; but in the summer 

 half-year, besides the maximum rate of barometric fall which occurs 

 with a wind from E, there is a second inferior maximum fall when the 

 wind is from S b W. There are also two maxima in the rate with 

 which the pressure of dry air diminishes during the summer. They 

 are of equal magnitude — -0131 and also occur with winds from 

 E and S b W. 



The most rapid changes, together with the winds that accompany 

 them, are shewn in the following tables : 



BAROMETRIC PRESSURE. 



Most rapid rise 

 Most rapid fall ■] 



SUMMER, 



Change in 



2 liours. 



+ •0162 



0113 



0093 



Wind. 

 WNW 



SbW 



WINTER. 



Change in ^- , 

 2 hours. ^*^'^'^- 



-{-.0214 NWbW 

 — •0343 EbS 



PRESSURE OP DRY AIR. 



Most rapid rise 

 Most rapid fall \ 



Change in 

 2 hours, 

 -f •023'7 



— •0131 



— •0131 



Wind. 

 WNW" 



E 

 SbW 



Change in 

 2 hours. 

 + •024*7 



— •osvg 



Wind. 



NWbW 

 EbS 



PRESSURE OF VAPOUR. 



Most rapid rise 

 Most rapid fall 



SUMMER. 



Change in ^. , 



2 hours. "™^^ 



+ •0042 S 



— •0079 WblSriN 



Wind. 



■WINTER. 



Change in 

 2 hours. 

 -t-^OOSY EbSiS 

 —•0038 NW^W" 



TEAR. 



Change in 



2 hours. 



+ •0194 



— •0218 



Wind. 



NWbW^W 

 E 



Wind. 



YEAR. 



Change in 

 2 hours. 

 + •0239 NWbW^W 

 — •0244 E 



Wind. 



Change in 

 2 hours. 

 + •0087 SSE^E 

 — •0054 NWbW^W 



