46 lftature'0 



"weather man" makes mistakes in his prog- 

 nostications; so true is this that it is never 

 safe to plan a picnic for to-morrow based upon 

 the predictions of to-day. The chief difficulty 

 in the way of solving the great problems relat- 

 ing to the sudden changes in the weather and 

 temperature lies in the fact that two-thirds or 

 more of the earth's surface is covered with 

 water; thus making it impossible to establish 

 stations for observation that would be evenly 

 distributed all over the earth's surface. 

 Enough is known, however, to make the study 

 of meteorology a most wonderfully interesting 

 subject. 



We have already stated that air is com- 

 posed of a mixture of oxygen and k&fe&gen. 

 chiefly, with a small amount of carbon dioxide. 

 So far as the life and health of the animal is 

 concerned we could get along without this 

 latter substance, but it seems to be a necessity 

 in the growth of vegetation. There are other 

 things in the air which, while they are unneces- 

 sary for breathing purposes, it will be well for 

 us to understand, as some of them are things 

 to be avoided rather than inhaled. 



As before mentioned, air contains moisture, 

 which is a very variable quantity. In a cold 

 day in winter it is not more than one-thou- 

 sandth part, while in a warm day in summer 

 it may equal one-fortieth of the quantity of 

 air in a given space. There is also a small 



