86 Experimental Philosophy. [Lecture 7. 



that, during the day, there is a current of air to- 

 wards the sea, and at evening the current sets in 

 from the sea to the land. The reason of this is, 

 that water is always of a more even temperature, 

 that is, of a more equal heat, than land. During 

 the day, therefore, the land becomes considerably 

 heated, and the air is rarefied ; the consequence 

 is, that in the afternoon a breeze sets in from the 

 sea, which is less heated. On the contrary, dur- 

 ing the course of the night the land loses its heat, 

 while that of the sea continues more nearly the 

 same. Towards morning, therefore, a breeze re- 

 gularly proceeds from the land towards the ocean, 

 where the air is warmer, and consequently more 

 rarefied, than on shore. 



The monsoons are periodical winds which 

 blow between the tropics, and which, though 

 the theory of them is rather more complicated, 

 originate in the same cause. They depend, in- 

 deed, upon large tracts of territory being heated 

 during the warm season, by which the general 

 course of the trade winds is partially interrupted. 

 Thus, when the sun approaches the tropic of 

 Cancer, the soil of Persia, Bengal, China, and 

 the ad joining countries, is so much more heated 

 than the sea towards the southward of these 

 countries, that instead of the usual trade wind, 

 the current of air proceeds at that season from 

 the south to the north, contrary to what it would 

 if no land was there. But as the high moun- 

 tains in Africa, during all the year, are extremely 



