6 THE PRINCIPLES OP AGRICULTURE 



duction of agricultural products rests upon 

 the application of many principles and facts of 

 natural science ; and the importance of such 

 application is rapidly increasing, with the com- 

 petitions and complexities of civilization. The 

 study of these natural sciences also establishes 

 habits of correct thinking, and opens the mind 

 to a larger enjoyment of life, — for happiness, 

 like success, depends upon habits of thought. 

 The farmer should live for himself, as well as 

 for his crops. The sciences upon the knowledge 

 of which the best agricultural jDractice chiefly 

 depends may now be mentioned, being stated 

 approximately in the order of their importance 

 to the actual practice of the modern farmer. 



14. Physics. The physical properties and 

 actions of bodies are fundamentally concerned 

 in every agricultural result, whether the farmer 

 knows it or not. The influences of light and 

 heat, the movements of fluids in soil, plant and 

 animal, the fbrces concerned in every machine 

 and appliance, are some of the most obvious of 

 these physical problems. So important to the 

 farmer is a knowledge of physics that "agricul- 

 tural physics" is now a subject of instruction 

 in colleges. The most important direct applica- 

 tion of a knowledge of physics to agricultural 

 practice has come as a result of recent studies 

 of the soil. The questions of soil moisture, soil 



