LONDON FOG. 225 



A. Because water does not cool down 

 at sun-set, so fast as the land does ; and, 

 therefore, the air in contact with it is 

 warmer. 



Q. Why does not WATER cool down so fast as 



LAND? 



A. 1 st Because the surface of water 

 is perpetually changing, and as fast as one 

 surface is made cold, another is presented : 

 and 



2ndly The moment water is made 

 cold it sinks, and warmer portions of 

 water rise to occupy its place : therefore, 

 before the surface of water is codled, the 

 whole volume must be made cold ; which 

 is not the case with land.- 



Q. What is the cause of a "pea-soup" 



LONDON FOG ? 



A. These fogs (which occur generally 

 in the winter time) are occasioned thus : 

 Some current of air (being suddenly 

 cooled) descends into the warm streets, 

 preventing the rise of the smoke, and 

 forcing it back in a mass towards the 

 earth. 



Q. Why are there not ALWAYS FOGS every 

 night ? 



