254 ESSAY 



its upper surface to the heavens, would remit 

 somewhat less heat to the grass beneath, than 

 what it received from that substance. But still, 

 as the sheltered grass, notwithstanding these 

 drawbacks, was upon one night, as may be col- 

 lected from the preceding relation, 8, and upon 

 another 1 1, warmer than grass fully exposed to 

 the sky, a sufficient reason was now obtained 

 for the utility of a very slight shelter to plants, 

 in averting or lessening injury from cold, on a 

 still and serene night. 



In the next place ; in order to learn whether 

 any difference would arise from placing the 

 sheltering substance at a much greater distance 

 from the ground, I had 4 slender posts driven 

 perpendicularly into the soil of a grass field, 

 and had them so disposed in other respects, 

 that their upper ends were 6 feet above the 

 surface, and formed the angular points of a 

 square having sides 8 feet in length. Lastly ; 

 over the tops of the posts was thrown an old 

 ship flag of a very loose texture. Concerning 

 the experiments made by means of this arrange- 

 ment of things, I shall only say, that they led 

 to the conclusion, as far as the events of dif- 

 ferent nights could rightly be compared, that 

 the higher shelter had the same efficacy with 

 the lower, in preventing the occurrence of a 

 cold upon the ground, in a clear night, greater 



