MOLECULAR DYNAMICS. 377 



the most refined researclies give unvarying results. Suppose we reverse 

 this experiment, and, commencing with nine pounds of ice, we will, by a 

 process of mental abstraction, again bring our conceptions down to the 

 immeasurably small, and fix our attention upon the molecules of the ice. 

 Figure to yourself the atoms of each molecule as being in oscillation 

 through points of equilibrium. And, while your attention is centred 

 upon the motions taking place in the interior of the mass, we will let 

 fall upon the block of ice a concentrated beam of sunlight, and see 

 how it deals with the inherent forces of cohesion and chemical affinity. 

 The solar undulations impinge upon the molecules of the ice, and, 

 under this bombardment of heat waves, see how rapidly the atoms 

 accelerate their motions ! All this wliile the contest is going on be- 

 tween the dynamic energy of the sun's waves of heat and the cohesive 

 force of the molecules. Beautifully and symmetrically the forces of 

 Nature built up the crystalline mass, and as silently and surely the 

 sun's competency of heat Avill effect its liquefaction. Thus far we have 

 seen the atoms accelerating in velocity by virtue of the energy imparted 

 by the solar-heat waves, and all this time they are vibrating within the 

 definite limits of the molecule. A further increase of heat will increase 

 the motion of the atoms, thus tending to a rupture of the bonds of 

 cohesive attraction. The struggle goes on until the ice melts, by which 

 process we have solar energy conserved in the latent heat of water. 

 The molecules being thrown almost beyond the range of cohesive 

 force, their movements are no longer confined to their former limits, 

 but may extend throughout the length and breadth of the mass. This is 

 the fluid state. The amount of energy required to swing the atoms 

 so nearly beyond the range of cohesive attraction, or simply to melt 

 the ice, is equal to 500 tons raised one foot high. This force still 

 exists as transmuted energy, and is the latent heat of water. A fur- 

 ther addition of heat takes the form of increased vibratory action up 

 to the boiling-point. Then comes another struggle seven times greater 

 than the first. This last remnant of cohesive force of water must; be 

 surrendered, and the heat-energy necessary to perform the act is con- 

 served or transmuted into the latent heat of steam. The last vestige 

 of cohesive force now being gone, the molecules of steam are free to 

 oscillate in all directions, and impinge against the walls of the contain- 

 ing vessel. If we continue the application of heat to the point of dis- 

 sociation, the molecules of vapor will have acquired a momentum suffi- 

 cient to rupture the bonds of chemical affinity. And here the energy 

 required to separate the molecules of steam into its constituent atoms 

 of oxygen and hydrogen is simply prodigious, being about forty-eight 

 times as much as was necessary for the process of liquefaction. Thus 

 the aggregated energies required to set free the oxygen and hydrogen 

 in our nine pounds of ice are equivalent to the raising of a ton's weight 

 28,000 feet, and we now have the original nine pounds of gas, laden 

 with the potential energies of 56,000,000 foot-pounds, which is just 



