318 Dynamic Theory. 



am pies of this may be met with by the myriad. For a few favored 

 races that appear to thrive and be in the ascendant, hundreds are re- 

 duced to the verge of a precarious existence. The tendency now ap- 

 pears to be to eliminate all animal races except our own. 



CHAPTER XXXY. 



ENERGY. 



It is now necessary to make an incursion into the region of physics, 

 in order to investigate the nature of the physical forces that assail the 

 organism, impose its habits upon it, and set up in it the movements that 

 produce the functions of sense and their accompanying differentiations. 

 Bodies possess two obvious modes of motion. One is motion in the 

 mass or molar motion, as, when a ball is thrown, it moves as a whole, 

 while its particles or component molecules may retain their position with 

 relation to each other. The other is molecular motion, or the movement 

 of the particles or molecules with reference to each other,' while the mass 

 as such may be either in motion or at rest. Molar motion is frequently des- 

 ignated as "work" by physicists. The distinctions made between the dif- 

 ferent motions relate to the bodies moved and the manner in which they 

 move. For example, the movement of a body from above toward the earth 

 we call falling ; a body going the other way is said to be rising. One 

 movement of a horse's legs we call a trot, another a walk, another a kick. 

 A bird flies, a fish swims. Such motions as these are in scientific parlance 

 called work. When work is done it is simply an expression of some 

 sort of energy that went before. Work does not do itself, or spring 

 from no-work. The work of a steam engine is due immediately to heat ; 

 and heat has been proved to be a mode of motion of the molecules of 

 bodies. The heat is created by burning wood or coal, which is chemical 

 process, also molecular. So we see that work or molar motion may 

 arise from molecular motion. In fact the motions are in reality only 

 one energy, driving first the molecules of a body in an invisible manner, 

 and then going over to another body and driving it in a visible manner ; 

 just as it is the energy of the same peck of oats that expresses itself in 

 a trot one minute and a kick- the next. The universe consists of matter 

 in motion. As the matter appears to us in many subordinate forms, its 

 apparent motions differ to correspond, the form of each determining the 

 sort of motion it will take when driven. All the distinctive names that 

 are given are simply for convenience, and not to be understood as de- 

 scribing different things, but only one thing under different aspects. 

 That is, the same energy which is called heat in one body, because of 

 the peculiar way in which it affects it, is called work when transferred 



