138 ON ATMOSPHERIC AND BAROMETRIC 



the particles of water which constitute the cloud 

 evaporate — and as condensation previously heated 

 the land atmosphere, and made it lighter, so 

 evaporation now cools it and makes it heavier. 

 The former process caused the barometer to sink, 

 and the sea breeze to blow — the latter causes 

 the barometer to rise, first checks, and finally 

 stops the sea breeze. Cloud formation in the 

 former period produced so great an effect as to 

 counteract the influence of increasing vapour 

 pressure, which may be shewn to have existed at 

 the time, and in addition to lower the barometer 

 and produce the sea breeze ; and cloud evapora- 

 tion had, in the latter period, sufficient power to 

 overcome the influence of declining vapour pres- 

 sure, which was going on at the time in the 

 formation of dew near the surface, and to produce 

 the general results that have been stated. 



At ten at night, the air over the land is found 

 to be, principally, through the influence of cloud 

 evaporation in cooling the column, heavier than 

 it is over the sea — the atmospheric current once 

 more turns, and the air begins to flow from the 

 land to the sea — or the land breeze sets in. It 

 is feeble at first, but increases in strength, until 

 at day break, or about four or five o'clock it 



