150 A YEAR IN SCIENCE 



of years in order to determine the climate of that 

 region. 



There is a popular notion, especially among old peo- 

 ple, that the climate of the region in which they are 

 living is changing. Records of the climate extending 

 over long periods of time indicate that there is little 

 basis for this current impression. A few exceptional 

 seasons, an intensely cold winter or a very wet sum- 

 mer, make a greater impression and are consequently 

 the ones which are best remembered. 



The principal elements of climate are moisture, 

 wind, and temperature. In previous chapters we have 

 discussed the general distribution of wind and rainfall. 



FIG. 55. The amount of heat received depends upon the angle 

 at which the sun's rays strike the surface of the earth. The same 

 number of rays fall on a smaller area at A than at B. 



Effect of temperature on climate. Practically all 

 the heat which warms our atmosphere comes from 

 the sun. This is shown by the difference in tempera- 

 ture between day and night, and between that on a 



