1877.^ H. F. Blanford — Variation of Barometric Tides. 75 



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Legend on the Seal. 



The following papers were read : — 



1. Note on the Variation of the Barometric Tides in connection tvith diur- 

 nal Land and Sea Breezes. — By Henry F. Blanford. 

 (Abstract.) 

 Mr. H. F. Blanford said that one of the commonest and most familiar 

 illustrations of convection currents, given in Manuals of Physics and Me- 

 teorology, is that of the diurnal land and sea breezes. During the morning 

 hours the solar heat falling on the land, heats and expands the air resting 

 on its surface to a much greater extent than that resting on the sea. Sup- 

 posing then, that previously to this heating, the several strata were in 

 equilibrium, the result must be, that the isobaric planes will be disturbed 

 and made to incline towards the sea. At the ground surface this disturb- 

 ance will be very small, but will increase with increased elevation. A 

 further consequence will be that, above a certain level, a current of air will 

 flow from over the land to the sea, raising the pressure over the latter, and, 

 at the sea surface, raising it above the pressure on the land surface. A 

 return current will be generated in the lower strata of the atmosphere, 

 especially during the afternoon, and this constitutes the well known sea- 

 breeze. At night, owing to the cooling and contraction of the air over the 

 land, all these actions will be reversed. The isobaric planes will incline 



