5 82 THE POPULAR SCIENCE MONTHLY. 



and silver. Value is based on utility, but utility is not intrinsic in 

 any substance ; and a thing is only useful so far as it is supplied in 

 needful quantities at the right time, the degree of utility constantly 

 varying. And so, although we may get the value of x (gold and sil- 

 ver) in terms of y (other commodities), and the value of y in terms 

 of x, both x and y remain unknown and variable quantities, however 

 glibly we may talk about them. 



Although the same difficulty confronts us here that is met in all 

 attempts at the ultimate analysis of things, none the less is it im- 

 perative that there should be a fixity of standards, rigidly adhered to. 

 To define a pound avoirdupois is as difficult as to define a pound ster- 

 ling; but commerce and science are alike dependent upon absolute 

 adherence to certain standards of weight, and upon the assumption 

 that the law of gravitation, by which weight is determined, is in- 

 flexible. 



Until the indestructibility of matter and the persistence of force 

 were demonstrated, there was nothing absurd in the supposition that 

 matter could be created and annihilated, force produced and destroyed ; 

 and men of genius and learning vainly sought to turn dross to gold, 

 to find the elixir of life, to construct machines which should create 

 their own force. Modern chemistry has dispelled the dreams of the 

 alchemist ; physiology has determined the laws of waste and supply 

 and fixed pretty definitely the limitations of life; and the discoveries 

 of Meyer and Joule have shown the fallacy of perpetual motion. 

 These things are now pretty generally understood, although a lunatic 

 is still occasionally to be found who wastes his life because of his ina- 

 bility to comprehend them : but it is not so generally recognized that 

 the principle of the correlation of forces is universal; that it applies 

 rigidly to all human activities; and that it is quite as impossible 

 in economical dynamics as elsewhere to get something for nothing. 



That coins are simply stamped bullion, and that the purchasing 

 power of money is regulated by the quantity of pure metal only is 

 now conceded by all economic writers ; but the establishment of this 

 principle is comparatively recent. In early times most extraordinary 

 delusions prevailed on this subject, nor are they yet wholly dissipated. 

 It will be interesting and instructive to note some of the mutations 

 which have been caused in the world's coinage by the numerous royal 

 and legislative attempts to make a part equal to the whole. 



The coins of all countries seem to have been called by the same 

 name as the weights used in them, and to have originally contained 

 the quantity of metal indicated by their names. The coins used in 

 Greece, Italy, France, and England, weighed in the first instance just 

 a talent, an as, or pond, a livre, or a pound. 



The Roman as, or libra, at first contained twelve ounces of copper, 

 and was divided into twelve parts or uncice, a division which was main- 

 tained for a long time. It is not known who first falsified the certifi- 



