32 KANSAS ACADEMY OF SCIENCE. 



lent of work performed upon it to raise it to that position. The only difference in 

 the two cases is, that the boy cast the stone upward, while gravity hurled it back. 

 We might, with equal propriety, affirm that, after the stone cast over the ice had 

 come to rest, it had acquired '"energy of position," as to say a like thing of this 

 stone as it turns to descend from mid-air. Should the boy run over the ice after 

 the stone and push it back with his foot, starting slowly, but gradually increasing 

 his speed until he reached his first position, we all would consider this a new prob- 

 lem, having no connection whatever with the throwing of the stone; for the boy 

 might have returned with another stone equal in weight, and the result would have 

 been the same, so far as the necessary energy was concerned. Likewise must we 

 consider the return of the stone to earth a fact separate and distinct from the rising 

 of the stone. 



As the stone falls, we observe it acquiring increased energy, for its velocity is in- 

 creasing. This is only a further illustration of the transformation of energy of 

 gravity force to the energy of a moving mass. It is but another evidence that 

 gravity is a correlated force. 



"Potential" energy is sometimes defined as "energy of position," and in a popu- 

 lar text-book on physics we find the question: "What has become of the energy 

 expended in the building of the Egyptian pyramids?" The author does not give 

 the answer, but from the text it is evident that he would say that it is "stored" in 

 the stones as "potential" energy, or "energy of position." Now, how can position 

 have energy? or, how can matter have energy by virtue of "advantage of position?" 

 Nothing but matter can have energy, and then only by virtue of its motion. The 

 energy exerted in raising the stones to their present position is not in the stones, 

 but as they were lifted against the force of gravity that energy was transformed to 

 gravity energy. 



Sometimes "potential" energy is regarded as a form of suspended or arrested 

 energy. This conception is directly antagonistic to the law of conservation of en- 

 ergy, which teaches that the sum total of energy is a constant, never increased or 

 diminished. Now, if energy be arrested or suspended for a moment, is it not for 

 that length of time practically destroyed — gone out of existence — diminishing the 

 sum total to that extent? And if it may be arrested for one moment, why not for a 

 longer time — an hour? And if for an hour, why not for a day, a year? Why not 

 for eternity? Why may it not be annihilated? Clearly true energy cannot be sus- 

 pended for the smallest fraction of time. When motion of a mass is transformed to 

 heat of a mass by friction, for instance, there is absolutely no interval of time re- 

 quired for the transformation of any particular portion of the energy. It is now 

 motion, and now instantly it is heat. 



If this be truth, it may be asked whence the heat energy of burning coal? The 

 books say it is the solar heat and sunshine of ages ago "stored" in the coal as "po- 

 tential" energy. It is surprising that such a blunder should be so long-lived; for 

 consider now what takes place when a piece of coal burns. The coal of itself cannot 

 burn; it requires oxygen with which it may unite, and the process of combination 

 is called burning. Then why not affirm that the heat is derived from the potential 

 energy stored in the oxygen ? That certainly would be as reasonable as to declare 

 that the energy was started in the coal. Why not give the oxygen at least half the 

 credit of carrying all this power these ages? In the growth of the jilants which 

 were afterwards transformed into coal, the sun's rays of heat and light played an im- 

 portant part indeed in enabling the plant chlorophyll to sejiarate the carbon from 

 the oxygen of the carbon dioxide, derived, for the most part, from the surrounding 

 air; but by no means could the energy of that heat and light be "shelved," as it 



