224 Proceedings of the British Association. 



being 7° '77 in the clear season, and 3° '71 in the cloudy ; the mean 

 of the year being 5° "7. The tension of the vapour also exhibits the 

 general character of a single progression, increasing from a minimum 

 at the coldest hour to a maximum about the warmest : with a slight 

 irregularity at noon, requiring future confirmation. In the gaseous 

 pressure, however, we find a double progression distinctly marked ; 

 one maximum occurring at 10 hours and another at 22 hours : one 

 minimum at 4 hours another at 1 6 hours ; and this double pro- 

 gression is found both in the cloudy and in the clear season, with 

 only a slight difference in the hours of maxima and minima : the 

 principal maximum in the cloudy season being at 20 hours instead 

 of 22 hours, and the inferior minimum in the clear season being 

 at 12 hours instead of 10 hours. The range of its diurnal variation, 

 like that of the temperature, is more than twice as great in the clear 

 as in the cloudy season. Col. Sabine then proceeded to describe the 

 phenomena of the direction and force of the wind ; and finds, from 

 Dr. Buist's Report, that for 200 days in the year there is a regular 

 alternation of land and sea breezes ; and, therefore, there is a double 

 progression of the daily variations of the force of the wind during 

 these 200 days. The land breeze usually springs up about 10k. or 

 between 10^. and I4h. blows strongest and freshest towards day- 

 break, and gradually declines until about 22h. at which time it 

 changes, after a lull of an hour or an hour and a half. The sea 

 breeze then sets in — the ripple on the water indicating its com- 

 mencement ; being first observed close in shore, and only extending 

 gradually out to sea. The sea breeze is freshest about 2h. and 

 progressively declines in the evening hours. Col. Sabine then pro- 

 ceeded with an explanation of the facts : and showed their coinci- 

 dence with the principles, — including, as a necessary element, the 

 separation of the aqueous and gaseous pressures. He then showed, 

 that in the annual variations, the leading features are closely analo- 

 gous to those exhibited at Toronto, Prague and Greenwich, — viz. 

 a correspondence of the maximum of vapour pressure and a minimum 

 of gaseous pressure with the maximum of temperature, and of the 

 minimum of vapour pressure and maximum of gaseous with the 

 minimum of temperature ; and a similar march of the three varia- 

 tions — but the epochs or turning-points not in every case identical, 



