136 ON ATMOSPHERIC AND BAROMETRIC 



this fall of the barometer on the land, when, 

 from the action of the land wind, the air over the 

 land appears to be increasing in weight ? These 

 questions, it would seem, cannot be satisfactorily 

 answered on the temperature theory, and yet 

 they require to be answered, if we are to under- 

 stand the causes that are in operation to produce 

 the various results that have been traced. 



From what has been stated, it will have been 

 seen that after ten o'clock in the morning, some 

 cause comes into action, sufficiently powerful to 

 reduce atmospheric pressure on the land, and to 

 render the air there so light as to permit the sea 

 air to flow towards the land as the sea breeze. 

 This cause, I contend, is not to be found in the 

 warming of the surface of the land by the sun, 

 as has been supposed, — but in the conversion of 

 a part of the aqueous vapour of the atmosphere 

 into water by the formation of cloud, as I have 

 shown in my account of the formation of the 

 cumulous cloud. A consequence of this conver- 

 sion is the liberation of heat, which lightens the 

 whole atmospheric column in the locality. The 

 results are, a fall of the barometer over the land, 

 and a flowing in of the heavier air from the sea 

 as the sea breeze. The formation of cloud, on 



