t 



..#/' 



I 



72 Dr. Holyoke's Estimate of the Excess of Heat and Cpkl 



- * 



perhaps tliirtj five centuries ago. Its surface, excepting a- 

 bout a hundred ,or a hundred and fifty mile% more or less, 

 along the sea coast, is almost universally covered with thick, 

 and almost impenetrable forests, as is well known to every 

 one. And, as the same causes always produce the same 

 efi^ts, it seems very probable, that the forests of America, 

 are in some way or other, instrumental in producing that 

 extra degree of cold, for which our enters are so remark- 



I - 



able. 



F 



Taking this therefore for a probable supposition, let us 



pursue it, and inquire whether it be confirmed by reason 

 and experiment. 



Among the many happy discoveries in philosophy and 

 chemistry, with which the celebrated Dr. Priestley has o- 

 bliged the world, one of very great importance is ) <' the pro- 

 perty, which the leaves of all plants .and vegetables of every 

 kind possess, of yielding, m day light, air of a much purer 

 kind, freer from phlogiston, and fitter for respiration, than 



common atmospherick air : that they not only furnish large 

 quantities of such air, but have also the faculty of absorbing 

 phlogiston from air, when fouled by a mixture of it, so as to 

 gender the same salubrious and respirable, which was before 

 noxious and sufibcating; and thus become, in the hands 

 of the great Author of Nature, 'one grand corrector of those 

 impurities, which might, otherwise, so far increase. n,« to 



con- 



of 



taminate the whole mass of the atmosphere 4 and in process 

 -'* time render it totally unfit for respiration, and the sup- 

 port of animal life." This is a doctrine well established, 

 and needs no new proofs. 



All 



