2g6 



LIGHT, HEAT, 



Sect. XIII. i. 2, 



and bv 



heat Is detruded 



which heat may 



produce inflammation of the m 

 ture, by uniting it with the ( 



given out ; 



if it be of an inflammable 



xy 



gen of the atmofpl 



and th 



producing an edudlion of more heat from the oxygen, and greater in- 

 flammation of the burning body. 



2. Another eflential difference between light and heat confifl:s in 



the particular attraction of the former to oxy 



fomuch that by 



their union the combined or folid oxygen becomes changed into an 

 aerial, or gaflTeous ftate ; as conftantly occurs, when the fun fliines 

 on the hyper-oxygenated water, which is perfpired or exhaled from 



plan 



mentioned in Botanic Garden, Vol. I. Cant. IV 



But 



V 



addition of heat feems neceflary to the converfion of a folid or 



fluid body into an aerial or gafleou 



I fuppofe the fun's light 



the fame time by combining alfo with the water fets at liberty fome 



■ X 



latent heat from it, which gives wings to the oxygen. 



IS 



The water perfpired by plants, when expofed to the funfh 

 believed to be decompofed, as it efcapes from the fine extremities of 

 the exhalent or perfpirative vefl*els of plants ; and that the hydrogen 



is reabforbed by the mouths of thofe veffels, as explained in Botanic 



Garden, Vol. I. note 34. 



evinced by etiolated or blanched vegetable leaves becoming green, 



That this happens to a certain deg 



wh 



expofed 



the funflilne in a few days ; which is, I believe 



) 



produced by their retaining the hydrogen of the water they perfp 

 as it is decompofed by the fun's light. 



But it is alfo probable, that the perfpired fluid of pi 



cufly hyper-oxygenated in the vegetable circulation. 



mts IS previ- 

 Firfl:. becaufe 



there is never perceived any fmell of hydrogen to attend this procefs 

 of liberating oxygen by the fun's light. And fecondly, becaufe the fol- 

 lowing productions of oxygen gas by the fun's light are fimilar phe- 

 nomena ; though I fuppofe the points or hairs on vegetable leaves may 

 contribute to the efcape of the oxygen, as explained in Botanic Gar- 



V0I.I 



Sir 



\ 



I 



