ON DEW, &c. 273 



also placed upon the grassplat, and another was 

 laid upon the raised board, which had been 

 thinly covered with sand. All these arrange- 

 ments were not completed before lOh. at night. 

 At 1 h. in the morning, ice appeared in the 

 watch-glasses on the grassplat and raised board ; 

 the heat of the air, as measured by a naked 

 thermometer, being then, at 4 feet above the 

 ground, 39^, and at 7 feet, 40 J. At 2h. ice 

 was observed in the pans in the pit, while a 

 thermometer in the air, 2j feet above the 

 ground, was 36J . Shortly afterwards, ice 

 began also to form in the pans upon the grass- 

 plat. The temperature of grass, fully exposed 

 to the sky, was at the same time 30, while that 

 of the earth an inch below the bottom of the 

 grass was 45. During the time of these ob- 

 servations dew formed copiously. 



EXPERIMENT 



My next attempt was in the manner men- 

 tioned by Mr. Williams. 



On the evening of the 22nd of May, I en- 

 compassed a square piece of level ground, the 

 sides of which were 3 feet long, with a border 

 of earth 4 inches high, and filled the area with 

 dry straw. On this were placed several of the 

 earthen pans, which had been formerly used, 



T 



