618 MISCELLANEOUS PAPERS. 



and the avoirdupois pouud only 665 graius lighter than the Babylonian 

 commercial miua; but, consideiing the origin of the metric system, it 

 is rather curious that the meter is only 1.97 inches shorter than the 

 Chaldean double royal cubit, and the kilogram only 102 grains heavier 

 than the Babylonian royal mina. Thus, without much exaggeration, 

 we may regard the present English and French fundamental units of 

 length and mass as representing, respectively, the commercial and royal 

 units of length and mass of the Chaldeans of four thousand years ago. 



Science tells us that the energy of the solar system is being slowl3^ 

 dissipated in the form of radiant heat; that ultimately the sun will grow 

 dim; life will die out on the planets; one by one they will tumble into 

 the expiring sun ; and at last darkness and the bitter cold of the abso- 

 lute zero will reign over all. In that far-distant future imagine some 

 wandering human spirit to have penetrated to a part of space immeas- 

 urably beyond the range of our most powerful telescopes, and there, 

 iTpon an orb where the mechanical arts flourish as they do here, let him 

 be asked to reproduce the standards of length, mass, and time with 

 which we are now familiar. In the presence of such a demand the 

 science of the seventeenth and eighteenth centuries would be power- 

 less. The spin of the earth which measures our days and nights would 

 be irretrievably gone ; our yards, our meters, our pounds, our kilograms 

 would have tumbled with the earth into the ruins of the sun and be- 

 come part of the debris of the solar system. Could they be recovered 

 from the dead past and live again ? The science of all previous ages 

 mournfully answers, No; but with the science of the nineteenth cen- 

 tury it is otherwise. The spectroscope has taught us that throughout 

 the visible universe the constitution of matter is the same. Everywhere 

 the rythmic motions of the atoms are absolutely identical, and to them, 

 and the light which they emit, our wandering spirit would turn for the 

 recovery of the long-lost standards. By means of a diffraction grating 

 and an accurate goniometer he could recover the yard from the wave 

 length of sodium light with an error not exceeding one or two thou- 

 sandths of an inch. Water is everywhere, and with his newly recovered 

 yard he could measure a cubic foot of it, and thus recover the standard 

 of mass which we call a pouud. The recovery of our standard of time 

 would be more difficult; but even that could be accomplished with an 

 error not exceeding half a minute in a day. One way would be to perform 

 Michelson's modification of Foucault's experiment for determining the 

 velocity of light. Another way would be to make a Siemen's mercury 

 unit of electrical resistance, and then, either by the British Association 

 method or by Lord Rayleigh's modification of Lorenz's method, find the 

 velocity which measures its resistance in absolute units. Still another 

 way would be to-fi^nd the ratio of the electro-static and electro-magnetic 

 units of electricity. Thus all the units now used in transacting the 

 world's business could be made to re-appear, if not with scientific, at 

 least with commercial, accuracy, on the other side of an abyss of time 



