126 A HISTORY OF 



CHAPTER XIX. 



AN ESSAY TOWAKDS A NATURAL HISTORY OF THE AIR. 



A LATE eminent philosopher has considered our atmosphere as one 

 large chymical vessel, in which an infinite number of various opera- 

 tions are constantly performing. In it all the bodies of the earth 

 are continually sending up apart of their substance by evaporation, to 

 mix in this great alembic, and to float awhile in common. Here mine- 

 rals, from their lowest depths, ascend in noxious, or in warm vapours, 

 to make a part of the general mass ; seas, rivers, and subterraneous 

 springs, furnish their copious supplies ; plants receive and return their 

 share ; and animals, that by living upon, consume this general store, 

 are found to give it back in greater quantities when they die.* The 

 air, therefore, that we breathe, and upon which we subsist, bears very 

 little resemblance to that pure elementary body which was described 

 in the last chapter ; and which is rather a substance that may be con- 

 ceived, than experienced to exist. Air, such as we find it, is one ol 

 the most compounded bodies in all nature. Water may be reduced to 

 a fluid every way resembling air, by heat ; which, by cold, becomes wa- 

 ter again. Every thing we see gives off its parts to the air, and has a 

 little floating atmosphere of its own round it. The rose is encompassed 

 with a sphere of its own odorous particles ; while the night-shade in- 

 fects the air with a scent of a more ungrateful nature. The perfume 

 of musk flies off in such abundance, that the quantity remaining be- 

 comes sensibly lighter by the loss. A thousand substances that escape 

 all our senses, we know to be there ; the powerful emanations of the 

 load-stone, the effluvia of electricity, the rays of light, and the insinu- 

 ations of fire. Such are the various substances through which we 

 move, and which we are constantly taking in at every pore, and re- 

 turning again with imperceptible discharge. 



This great solution, or mixture of all earthly bodies, is continually 

 operating upon itself; which, perhaps, may be the cause of its unceas- 

 ing motion : but it operates still more visibly upon such grosser sub- 

 stances as are exposed to its influence ; for scarcely any substance is 

 found capable of resisting the corroding qualities of the air. The air, 

 say the chymists, is a chaos, furnished with all kinds of sails and men- 

 struums ; and, therefore, it is capable of dissolving all kinds cf bodies. 

 It is well known, that copper and iron are quickly covered, and eaten 

 with rust ; and that in the climates near the equator, no art can koop 

 them clean. In those dreary countries, the instruments, knives, and 

 keys, that are kept in the pocket, are nevertheless quickly encrusted ; 

 and the great guns, with every precaution, after some years, become 

 useless. Stones, as being less hard, may be readily supposed to be 

 more easily soluble. The marble of which the noble monuments of 

 Italian antiquity are composed, although in one of the finest climates 

 in the world, shew the impressions which have been made upon them 

 .ky the air. In many places they seem worm-eaten by time ; and, in 

 ethers, they aouear crumbling into dust. Gold alone seems tc be ex 



* Boyle, vol. ii. p. 593 



