MOLECULAR DYNAMICS. 375 



of those files of men, it being the individual duty of each man to re- 

 tard the momentum of the* ball by interposing his hand in its path. It 

 is evident that each hand so interposed will receive a shock, the force 

 of which is just equivalent to the amount parted with by the ball itself. 

 Finally, the ball comes to rest. The original momentum of the ball has 

 for its equivalency the sum total of the lesser energies imparted to the 

 several hands interposed. Or again, if, instead of hands interposed, we 

 substitute a row of smaller balls, and let them receive the impact of 

 the moving one, the result will be just the same. Each and every ball 

 interposed will have the motion of its constituent particles augmented 

 by an amount of energy of motion exactly equivalent to that parted 

 with by the larger ball ; and, when the moving ball finally comes to 

 rest, the sum total of molecular energies in the interior of each ball is 

 exactly equal to the original momentum of the larger ball. Thus we 

 have an illustration of the transference of molar into molecular motion, 

 the molecular motion making its appearance as heat, one of the modes 

 of force. If you push endwise against a stick of wood, the force ap- 

 plied will immediately appear at the other end. This is transmission 

 of force by means of molecular action. The force being applied to one 

 end of the bar is transmitted from particle to particle with great veloci- 

 ty its entire length. If a row of bricks be properly placed, any force 

 applied to the first of the row, sufficient to topple it against the next, 

 will be transmitted throughout from the first to the last of the series. 

 Or again, if the bar of wood be pushed against one end of our imagi- 

 nary row of bricks, we shall have in the rod and in the falling bricks a 

 continuous chain of similar phenomena, the action of the bricks being 

 a visible illustration of the transmission of force, and highly analogous 

 to that invisible transmission along the molecules of the bar. 



Apart from the difi"erent modes of force, we have energy in two 

 forms — static or potential, and actual or dynamic. The potential has 

 been likened to a weight wound up, and the actual to a weight in the 

 act of falling. The amount of energy expended in winding up the 

 weight, less the friction, is exactly equivalent to the potential energy 

 of the weight so raised, also to the dynamic energy given out by its 

 falling or running down. The inherent measure of force possessed by 

 each and every atom is its kinetic energy, and this energy is the cor- 

 relative and antecedent of all the modes of force which characterize 

 the various phenomena of the visible universe. The condition in which 

 matter presents itself to our senses depends upon the degree in which 

 these several forces are made manifest. All the phenomena of Nature 

 consist in transformations of energy only, the working force of the uni- 

 verse being previously invested in the kinetic energy of its atoms. 



The potential energies of the atoms of matter, in their free condi- 

 tion, are almost beyond human comprehension. Thus, heat a pound of 

 charcoal to the point of incandescence. The vibratory motion of the 

 atoms of carbon will then have reached an amazing velocity ; oxygen 



