ON DEW, &c. 225 



Upon the summit, which may, in some measure, 

 account for the last-mentioned observation of 

 Aristotle, as far as relates to what happens in a 

 clear night. 



The height of the hill, in this example, has 

 been supposed to be small, to make it accord 

 with that of the stations, whose temperatures 

 were compared by Mr. Six with the heat of the 

 air near the ground. But observations of the 

 same kind will apply to hills of much greater 

 elevation. For granting, first, that the air at 

 the height of 220 feet is never more than 10 

 colder, than that near to the earth, which is not 

 probable, and is indeed contradicted by some 

 of Mr. Six's observations ; and again, that the 

 increase of the air's heat, in a calm and serene 

 night, ceases precisely at the greatest height, 

 to which Mr. Six carried his observations, which 

 is also improbable ; still a reduction, to the ex- 

 tent of 10, in the temperature of the air near 

 to the earth, will render the cold of this low 

 portion of the atmosphere greater than that of 

 any other portion, which is not more than 2500 

 or 3000 feet above the former, if the estimate 

 be just, which makes a declension in the heat 

 of the atmosphere of 1 for every 250, or 300 

 feet of its height, when no counteracting cause 

 exists. 



The remarks, however, which have been 



Q 



