ON DEW, &c. 153 



many times, during serene and still nights, exa- 

 mined the temperature of dewed grass, and 

 have constantly observed it to be less than that 

 of the air, anywhere between 1 inch and 9 feet 

 above the ground, the latter being the greatest 

 height, at which I ever marked the heat of the 

 atmosphere, in these experiments. I generally, 

 however, compared the temperature of dewed 

 grass with that of the air 4 feet above the 

 ground ; and on nights, that were calm and 

 clear, very frequently found the grass, at the 

 ordinary place of my observations, 7, 8, or 9 

 degrees colder than the air at that height. Se- 

 veral times it was 10 and 11 colder than the 

 air, and once 12. These differences are not 

 so great, as those related in Mr. Six's post- 

 humous work. But, in his experiments, the 

 temperature of grass was compared with that 

 of the air 7 feet above the ground, which, in 

 clear and calm nights, may be regarded as J a 

 degree warmer than the air at the height of 4 

 feet. Besides ; the most considerable differ- 

 ences, mentioned by Mr. Six, occurred in winter, 

 when he says a greater degree of cold is oc- 

 casioned by dew, than at any other time ; 

 whereas very few of my experiments, on the 

 temperature of grass, were instituted in that 

 season. In the last place ; my experiments 



