ON DEW, &c. 231 



tlian when this substance was in contact with 

 it, partly from having a small oblique aspect of 

 the sky, and partly from receiving air, which 

 has been cooled by passing over other grass 

 fully exposed to the heavens. 



When a piece of metal, having closely applied 

 to its under surface a substance of some thick- 

 ness, which attracts dew powerfully, and, there- 

 fore, imbibes readily heat that is radiated to it, 

 is exposed to the sky at night, the heat supplied 

 by the attached substance, both from its own 

 original store, and from what it has acquired 

 through the radiation of the ground to it during 

 the exposure, will enable this piece to resist 

 longer, than a bare piece, the formation of dew, 

 or even than another piece, which has only a thin 

 coat of matter considerably attractive of dew 

 attached to its underside. The experiment 

 with the wooden cross, covered with gilt paper, 

 affords an example of the latter fact. 



A very small metallic plate, suspended in the 

 air, is less readily dewed than a large one, 

 similarly situated, as it receives, in proportion 

 to its size, more heat from the atmosphere. 

 On the other hand, a very small plate laid 

 upon grass, rendered cold by radiation, will be 

 sooner dewed than a larger one in the same 

 situation, from presenting a greater propor- 

 tional circumference to the surrounding grass, 

 and therefore losing more quickly its heat by 



