When we examine our atmosphere, we find it is composed of oxygen and nitrogen. The nitrogen constitutes no less than 80 percent of the atmosphere; the remaining 20 percent, consists of oxygen, so that the atmosphere consists almost entirely of these two gases, odorless and colorless and invisible. The atmosphere is, however, never free from moisture; a certain amount of aqueous vapor is always present. The quantity can hardly be stated, as it varies from day to day and month to month; it depends upon the temperature and other conditions. Then we have the gas commonly called carbonic acid in extremely minute quantities, about one part in 2,500, or four one-hundredths of one percent. A small quantity of ammonia and a small quantity of ozone are also present.
Besides these gases which have been enumerated, and which play an important part in supporting life in both the kingdoms of nature, we find a great many solids. Many people know how dust settles upon everything about the house. This dust has recently been the subject of most active study, and it proves to be quite as important as the vital oxygen that actually supports life.

License information: nan
MPAA: G
Go to source: http://www.gutenberg.org/files/8687/8687-h/8687-h.htm#12