302 



LIGHT, HEAT, 



Sect. XIII. 1.6. 



the liberation of it, when expofed to the funifhine, which thus dif- 

 oxygenate the water by their united effe(fl. 



This appears on immerfinga dry hairy leaf in water 



frefli from 



pun:ip 



merabl 



I globules like quickfilver appear on almoft every 

 point ; for the extremities of thefe points attra6l the particles of wa- 

 ter lefs forcibly, than thofe particles attrad each other ; hence the 

 contained air, whofe elafticity was but jufl: balanced by the attractive 



power of 



furrounding part 



of water to each oth 



finds at 



the point of each fibre a place, where the refiftance to its expanfion 

 is lefs ; and in confequence it there expands, and becomes a bubble of 

 air. It Is eafy to forefee, that the rays of the funfhine, by being re- 

 fraded and in part refle6led by the two furfaces of thefe minute air- 



bubbles, muft impart to them much more heat 



rent water 



nd 



fac 



th 



en 



fcent by furth 



the tranfp 

 • expandir 



o 



them ; and that the points of vegetables attradt the particles of water 



feen by 



fph 



form of 



lefs, than they attra6l each other, is 

 dew-drops on the points of grafs. 



6, It may be added in this place, that there may alfo be a fallacy 

 in the fuppofed refults of thofe experiments, where plants have been 

 confined in hydrogen or azote mixed with atmofpheric air j and have 



been believed to have vegetated more vigoroully, and to h 



me 



liorated the air. In thefe experiments I fufped, that the impure part 

 of the air was attracted by the water, and taken up by the abforbents 

 of the roots of the plants from the water, rather than by the abforbents 

 of their leaves or ftems in the air; and that the melioration of the air 

 was occafioned, as above ^efcrlbed, by the adion of the light on the 

 water perfpired from the furface of the plant, or liberated by its 

 points from the water, with which part of it was covered. This is 

 rendered more probable, becaufe plants and feeds In the experiments 



to vegetate In thofe gaffes, which were totally de- 



of others ceafed 



prived of oxygen, as in M. Scheele's experiments on the growth of 

 feeds. 



IL I . The 



