.1. 



r. 



•>th 



at 



ins 



at 

 as 



^entu 



tade, 

 hat; 



in 



ewn 



IS alfo 

 )neous 



u 



pple, 



C7,as 



;nt by 

 found 



w 



r 



air, HI 

 •xhala- 

 hich 



I veiTel 

 whole 



elude, 

 fcrbed 



> again 





fpond 

 It they 



their 



iratory 



cq 



uire 



J, tl^^^ 



^^ 



Sect.1V. I. 2. 



AND VEINS. 



41 



eledricity is (hewn by experiments to defcend through the ft 



and that if the final caufe of 



of trees, except in thunder ftornis ; 



o-etable leaves had been to condudl eledf icity from the air, they ougb 



to have been gilded leaves with metalHc flems. 



Others ao-ain have fuppofed that the leaves of plants; acquire 

 phlogiftic material from the fun's light, whence it was believed th^ 

 on this account they turn their upper furfaces to the fun. But thoug 



a 



yet if th 



final 



lio-ht is more or lefs attracted by all opake bodies, 



caufe of vegetable leaves had been to abforb light, they ought to have 



been black and not orreen ; as by Dr. Franklin's experiment, who laid 



fhreds of 



fnow in the fun-{h 



the black funk 



much deeper than any other colour, and confequently abforbed much 



The ufe of light in vegetable refpiration will be treated 



more light. 



of in Sea. XIII. 



2. The air of our atmofphere has been fhewn by the experiments 

 of Prieftley, Cavendifh, and Lavoifier, to confifl of twenty-feven 

 parts of refpirable air, called oxygene gas, with feventy-three parts of 



termed 



gas, which are mixed togeth 



water coniifts of eighty-fi 



unrefpirable air, 



chemically combined ; wh 



dreth parts of oxygen to fifteen of hyd 



flate of combination, and are not therefore fit for refp 



not 



which 



fl 



in 



hi] 

 th 



B 



water a confiderable quantity of common 



fcap 



on 



boil 



a 



and, even pure vital air was difcovered 



alfo diffolved, which 



in the 



f 



water of fome fprings by fir Benj.Thomfon, when it was expofed 

 the fun's light. Philofoph. Tranfadt. The former of thefe fluids 



th 



dapted to the refp 



f 



nimal 



d th 



ihat of aquatic 



d the analogy between the aerial and aquatic 



leaves of vegetables and the luno;s and pjills of animals embraces fo 



o _ 



It to 



many circumfi:an 



that we can fcarcely withhold our afie 



performing fimilar ofii 



The internal furface of the air-veffels of the lungs of men are faid 



or about fif- 



be equal to the external furface of the whole body 



G 



teen 



