Dr. Holyoke's Estimaie of the Excess of ITcat ami Cold. 87 



mineral^ which are thus heated. Whence it seems to follow, 

 that it is far from certain that any such pure air, or indeed 



F 



any air at all; is derived from the leaves of plants exposed to 

 the suu; as was suggested and seemed to be proved, by the 

 experiments of Drs, Priestley, Ingcnhousz, and -others. If 

 this be really the truth of the case, and air is not produced 

 from the leaves of vegetables, vd in the paper just now men- 

 tioned I have suppo.sed it to have been ; then, all the subse- 

 quent reasoning upon this hypothesis is void of foundation, 

 and must fall to the ground. But it ought to be noted, Ihut 

 the facts and observations contained in the Edunate, which 

 shew our atmosphere to be really drier than the European, 

 are not at all affected by the failure of this hypothesis, but 

 remain in their full force, though I may have mistaken the 

 cause, when I attributed it to the purity .of the air derived 

 from the leaves of vegetables. 



Further, since writing the 

 accidentally been informed of a fact, which confirms the • 

 idea, that our evergreens are, if not the cause of dephlogis- 



papei' before mentioned, I 



ticating the air, yet somehow the cause of an increase of cold. 

 The fact I mean is, that frosts are commonly observed to appear 

 much earlier every aidumn, as well as later in the spring, in the 

 neighhourhood of 2me and other evergreen ivoods, than in other 

 places, or than in the neighhourhood of other ivoods which drop 

 their leaves in the winter. And this I find confirmed by eve- 

 ry one I have since inquired of, who.^e business or situation 

 leads them to attend to the matter; and I am told, it is a 



Common 



observation, though I confess I never hearcl of 



before I presented the paper to the Acadcm} 



If 



I. 



• 



♦ 



