THE EARTH. 273 



But there is no animal whose frame is more 

 sensibly affected by the changes of the air than 

 man. It is true, he can endure a greater variety 

 of climates than the lower orders generally are 

 able to do ; but it is rather by the means which 

 he has discovered of obviating their effects, than 

 by the apparent strength of his constitution. 

 Most other animals can bear cold or hunger 

 better, endure greater fatigues in proportion, and 

 are satisfied with shorter repose. The variations 

 of the climate, therefore, would probably affect 

 them less, if they had the same means or skill 

 in providing against the severities of the change. 

 However this be, the body of man is an instru- 

 ment much more nicely sensible of the variations 

 of the air, than any of those which his own art has 

 produced; for his frame alone seems to unite all 

 their properties, being invigorated by the weight 

 of the air, relaxed by its moisture, enfeebled by 

 its heat, and stiffened by its frigidity. 



But it is chiefly by the predominance of some 

 peculiar vapour, that the air becomes unfit for 

 human support. It is often found, by dreadftd 

 experience, to enter into the constitution, to mix 

 with its juices, and to putrefy the whole mass of 

 blood. The nervous system is not less affected 

 by its operations ; palsies and vertigoes are caus- 



Though numerous experiments have been made in order to ascertain the 

 exact proportions of oxygen and nitrogen composing the atmospherical or 

 common air, they have not yet been determined ; and " nothing can decide 

 these fundamental chemical proportions, except a new, elaborate, and mi- 

 nutely accurate series of experiments. We shall then know whether the at- 

 mosphere contains in volume 20 or 21 per cent of ^oxygen." URB'S Chemical 

 Dictionary. AIR.] 



VOL. I. S 



