2 GEAVITY, AND ITS EFFECTS. 



formative, sometimes destructive, we continue to 

 witness at the present day. 



Two of these powers, which work throughout 

 the entire universe, and bring under each other's 

 influence all the heavenly bodies — Gravity and Heat 

 — stand out as the mainsprings both of the past 

 revolutions, and of the present changes of the 

 earth. 



Gravity is the principle of attraction and so- 

 lidity; Heat of expansion and mobility. All 

 material tilings bear within them these two sources 

 of action. On the one hand, Science points to 

 gravity as an attractive force, put forth by all 

 bodies alike — a force acting with a strength which, 

 for any given distance, is always the same, but which 

 is lessened as the distance is increased. On the 

 other hand, it reveals to us heat as a principle 

 subtle in the extreme, which penetrates the sub- 

 stance of all bodies more or less easily, and accu- 

 mulates in them to a greater or less amount ; it 

 issues again from these bodies, when it does escape, 

 in rays, that is, in straight lines, diverging from 

 each other in all directions. The intensity of the 

 heat-rays also is lessened as the distance from 

 their source is increased, according to the same 

 law as that which governs gravity. 



General Gravity (gravitation) — the mutual at- 

 tracting power of all heavenly bodies — links the 

 earth with its companion, tlie moon, and leads the 



