23 FRAGMENTS OF SCIENCE. 



potential. It is then drawn toward &quot;its neighbor with 

 accelerated speed, thus, by attraction, converting its poten 

 tial into dynamic energy. Its motion in this direction is 

 also finally checked, and, for an instant, again its energy is 

 all potential. It again 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 

 :ui(l fro in her yearly journey round the sun, is also true of 

 her minutest atom. We have w r heels within wheels, and 

 rhvlhm within rhythm. 



When a body is heated, a change of molecular arrange 

 ment always occurs, and to produce this change heat is 

 consumed. Hence, a portion only of the heat communi 

 cated 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 generate*! ; but the heat, or molec 

 ular dynamic energy, developed at the moment of collision, 

 is not the equivalent of the sensible dynamic energy de 

 stroyed. The true equivalent is this heat, plus the potential 

 energy conferred upon the molecules by the placing of 

 greater distances between them. This molecular potential 

 energy is afterward, on the cooling of the body, converted 

 into heat. 



Wherever two atoms capable of uniting together by 

 their mutual attractions exist separately, they form a store 

 of potential energy. Thus our woods, forests, and coal 

 fields on the one hand, and our atmospheric oxvuvn on the 

 other, constitute a vast store of energy of this kind vast, 

 but far from infinite. We have, besides our coal-fields, 

 bodies in the metallic condition more or less sparsely dis 

 tributed in the earth s crust. These bodies can be oxidized, 

 and liemv are, so far as they g&amp;gt;, stores of potent ial energy. 



