INTRODUCTION. 



So far as human agency goes, these chemical elements 

 are indestructible as to quantity, and not convertible 

 one into another. 



We distinguish various natural manifestations of force 

 which, acting on or through matter, produce all material 

 phenomena. In the subjoined scheme the recognized 

 forces are to some extent classified and defined, in a man- 

 ner that may prove useful to the reader. 



- Repulsive 



\ Att ctive 



distances I 



Act only at 

 insensible 

 distances 



Attractive 



Within human experience the different kinds of force 

 are mostly convertible each into the others, and must 

 therefore be regarded as fundamentally one and the same. 

 Force, like matter, is indestructible. Force acting on 

 a body may either increase its Kinetic Energy, or be 

 stored up in it as Potential Energy. Kinetic (or ac- 

 tual) energy is the energy of a moving body. Potential 

 (or possible) energy is the energy which a body may be 

 able to exert because of its state or position. A falling 

 stone or running clock gives out actual energy. The 

 stone while being raised, or the clock while winding, ac- 

 quires and stores potential energy. In a similar manner 

 kinetic solar energy, reaching the earth as light, heat and 

 chemical force, not only sets in operation the visible ac- 

 tivities of plants, but accumulates in them a store of po- 

 tential energy which, when they serve as food or fuel, re- 

 appears as kinetic energy in the forms of animal heat, 

 muscular and uervous activity, or as fire and light. 



The sciences that more immediately relate to agricult- 

 ure we Physics, Chemistry and Biology. 



