520 THE THEORY OF ENERGY AND THE LIVING WORLD. 



done. Very interesting researches upon this matter were communi- 

 cated by the celebrated physicist, Coulomb, to the institute in the year 

 1797. A man of 70 kilograms average weight was occupied with as- 

 cending the stairs of a house 20 meters high. He made the ascension 

 at the rate of 14 meters a minute and kept up this rate effectively for 

 four hours. The work thus done was equivalent to 235,000 kilogram- 

 meters. But when instead of mounting without load the man was made 

 to carry a weight, the result was quite different. Coulomb's laborer 

 carried up 6 loads of wood in a day to a height of 12 meters in GG 

 trips. This would correspond to a maximum work of 109,000 kilogram- 

 meters, instead of 235,000. 



Energy, or mechanical work, may be discovered in two forms — actual 

 or kinetic energy, corresponding to a mechanical action being actually 

 performed, and potential energy, or energy in reserve. 



A body when raised to a certain height develops in its fall an 

 amount of work in kilogram-meters equal to the product of its weight 

 by the distance through which it falls. This work may be applied in 

 various ways. In this way, for example, public clocks are driven. JSTow, 

 when the weight is being wound up, when the works are lax, and no 

 motion occurs, the ancient physics would say that there was nothing 

 to consider. The phenomenon is the fall. That will take place, but 

 for the moment there is nothing occurring. 



In energetics the reasoning is different. The body is said to possess 

 a capacity for work which it manifests upon a suitable occasion ; it has 

 stored-up energy, the power of exerting energy, or potential energy. 

 When the body falls, this potential energy becomes transformed into 

 actual or kinetic energy. The work done by the weight in falling is 

 exactly equal and opposite to that done in wiuding the clock. This is 

 the source of the energy gradually expended in eight or fifteen days 

 in the regular movement of the hands and the striking of the hours. 

 The fall is the counterpart of the elevation. There is recovered in 

 the second phase of the phenomenon exactly the amount of energy 

 expended in the first. Between the two phases may intervene as long 

 a time as one pleases, during which the energy slumbers, as it were, 

 and of which we speak as a period of potential energy. Thus the con- 

 necting link between the phenomena is maintained ever present, and 

 the energy, never lost sight of in these conceptions, is not a new thing 

 when it reappears. Thus we conceive of energy as something real, 

 indestructible, and eternal, having an objective existence; sometimes 

 revealing itself, sometimes slumbering; now manifest, now latent. 



Similarly the flow of a torrent of water in a mountainous region may 

 be utilized to drive the water wheels and turbines of the mills in the 

 valley. The fall of the water produces mechanical work which would 

 be a creation ex nihilo if the antecedent phenomena were not taken 

 account of. It can be shown that this is but a case of restitution, for 

 the water was taken from the place to which it now returns, and raised 



