EELATION TO GEOGRAPHY AND ARITHMETIC. 287 



First. Earth forces, those agencies which are chan- 

 ging the earth and fitting it for the habitation of man. 



Second. Earth materials, the matter on which these 

 agencies or forces are acting. 



Third. Earth forms, the effect of the action of the 

 agencies or forces on the materials. 



If we emphasize in earlier years the life side of nature 

 study or geography, we shall dwell in our preparatory 

 work in geography in the primary grades on the agen- 

 cies acting on the earth, and first on those most easily 

 seen by the child. From the child's point of view the 

 most important earth forces are water, air, and heat. 

 Water and air are not really forces, but merely vehicles 

 upon and through which gravitation, heat, and other 

 forces act ; but from the child's point of view they are 

 most active agencies, producing, with the aid of heat, 

 most of the changes about him. 



It is best to begin with water, in the forms of vapor, 

 fog, clouds, mist, dew, rain, frost, snow, ice, streams, 

 and waves, and study its forms and work. The study 

 of water prepares for the study of air (including winds) 

 and both lead up to heat and its effects and influence 

 on the earth. 



The order recommended is : during two or three win- 

 ter months of the first school year, water; during the 

 same period of the second year, air; during the winter 

 of the third year, heat, including its sources and sim- 

 plest effects ; and during the fourth year, heat, studied 

 in a much broader way, preparing for the study of 

 physics in succeeding grades. 



