THE CONSTITUTION OF NATURE. 23 



bell of Westminster, when raised before striking, pos- 

 sesses potential energy; when it falls, the energy be- 

 comes dynamic; and after the stroke, we have the 

 rhythmic play of potential and dynamic in the vibra- 

 tions of the bell. The same holds good for the molecular 

 oscillations of a heated body. An atom is driven against 

 its neighbour, and recoils. The ultimate amplitude of 

 the recoil being attained, the motion of the atom in 

 that direction is checked, and for an instant its energy 

 is all potential. It is then drawn towards its neighbour 

 with accelerated speed; thus, by attraction, converting 

 its potential into dynamic energy. Its motion in this 

 direction is also finally checked, and again, for an in- 

 stant, its energy is all potential. It once more retreats, 

 converting, by repulsion, its potential into dynamic 

 energy, till the latter attains a maximum, after which it 

 is again changed into potential energy. Thus, what is 

 true of the earth, as she swings to and fro in her yearly 

 journey round the sun, is also true of her minutest 

 atom. We have wheels within wheels, and rhythm 

 within rhythm. 



When a body is heated, a change of molecular ar- 

 rangement always occurs, and to produce this change 

 heat is consumed. Hence, a portion only of the heat 

 communicated to the body remains as dynamic energy. 

 Looking back on some of the statements made at the 

 beginning of this article, now that our knowledge is 

 more extensive, we see the necessity of qualifying them. 

 When, for example, two bodies clash, heat is generated; 

 but the heat, or molecular dynamic energy, developed 

 at the moment of collision, is not the exact equivalent 

 of the sensible dynamic energy destroyed. The true 

 equivalent is this heat, plus the potential energy con- 

 ferred upon the molecules by the placing of greater 

 distances between them. This molecular potential en- 

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