22 WELLS'S NATURAL PHILOSOPHY. 



at the present day, is, that these forces, or agents, are not matter, but prop- 

 erties, or qualities, of matter. 



We see a stone fall to the ground, and say that the cause of it is the at- 

 traction of gravitation ; — we observe an object at a distance, and say that w© 

 see it through the action of hght on the eye ; — we notice a tree shattered by 

 lightning, and say it is the effect of electricity ; — we observe an animal or 

 plant to grow and flourish, and ascribe this to the action of the vital force. 

 But if it is asked, What is the original cause of gravitation, light, electricity, 

 and vital force? — the wisest man can give no satisfactory answer. If tba 

 Creator governs matter through the agency of instruments, these forces may 

 be called his agents, or tus instruments. ' 



CHAPTER III. 



INTERNAL. OR MOLECULAR FORCES. 

 What is an 28. An INTERNAL, Or MOLECULAR FoRCE, 18 



MoiJ"uiar°'^ one that acts upon the particles of matter only 

 v^^zoa'i at insensible distances. This variety of force 



differs from all others in this respect. 

 What is At- 29. The various changes which matter un- 

 traction and dorcToes, rcudcr it certain that the atoms, or 



Repulsion? . . 



particles of all bodies are acted upon by two 

 distinct and opposite forces, one of which tends to draw 

 the atoms, or particles, close together, while the other 

 tends to separate them from one another. The first of 

 these forces we call Attraction, the second Repulsion, 

 both acting at insensible distances. 



A blade of steel, or a thin piece of wood, when bent within 

 Give an ex- i r- -i ^ 



ample of At- a certain limit, will, when the restraint is removed, restore it- 

 acting °at an ^^^ *° ^'^ original form. This takes place through the agency 

 insensible dia- of an internal force, attracting the particles together, and tend- 

 ing to keep them in their original place. 



whatisEias- 30. ELASTICITY is that property of matter 

 •^"'y^ which disposes it to resume its original form 



and shape, after having been bent or compressed by some 



external force. 



Elasticity, therefore, is not so much a distinct property of matter, as ia 



usually stated, as it is a phenomenon of attractive and repulsive forces. 



