220 BOARD OF AGRICULTURE. 



heat. The air is heated slightly if at all by the passage of the 

 sun's rays through it. The heat is conveyed to the upper re- 

 gions in two modes, radiation and connection. By the former 

 the heat passes from the earth in all directions like the spokes of 

 a wheel and moves in an opposite direction from the wind as 

 well as with it. Thus we feel the heat from a grate by radiation, 

 though the air is passing directly from us to the grate. The 

 most efficient mode of heating the great volume of air that sur- 

 rounds the earth is by connection, that is, the particles of air 

 coming in contact with the heated earth are expanded, become 

 lighter than the other particles and consequently rise, while 

 others take their place, and in their turn rise. 



Besides the influence which light, heat and moisture exert 

 upon the climate of a country, the air also contains quite a frac- 

 tion, about one twenty-five hundredth part of its volume, of 

 carbonic acid, which is quite a constant proportion. Tiie quan- 

 tity of ammonia in the air is very variable, being the largest af- 

 ter a long, warm, dry time, and the smallest after a long con- 

 tinued rain, as this gas is very soluble in water, and comes down 

 with every shower to fertilize the earth. There are also various 

 other gas^s constantly rising from the surface of the earth and 

 mingling with the air, in which also float innumerable sporules 

 or seeds, and even minute particles of metals and other inor- 

 ganic matter, but in such small quantity as almost to escape the 

 tests of the chemist. 



Climatology is a subject worthy of investigation, and has not 

 received that attention, either from farmers or scientific men, 

 which its importance demands. In the air, as wonderfully 

 made by our Creator, " we live, and move, and have our being." 

 We can live without food for many hours, and even days ; but 

 we cannot live without the air a single moment. All the infe- 

 rior animals and all plants are equally dependent with man 

 upon the atmosphere for their existence. A mouse, put under 

 the receiver of an air-pump, gasps and dies as the air is ex- 

 hausted, and not a seed germinates in the ground unless the air 

 has access to it and gives it vitality. Air is so common and 

 such an abundant blessing that we do not think sufficiently of 

 its value. Like water, it is so free that we forget to be grateful 

 for it ; and while it is so wisely contrived for our health and 

 comfort, the seeds of disease and death are often, by our igno- 



