Standard Measures
OF
UNITED STATES,
GREAT BRITAIN, AND FRANCE.
HISTORY AND ACTUAL COMPARISONS.
WITH
APPENDIX ON INTRODUCTION OF THE MÈTRE.
BY
ARTHUR S. C. WURTELE,
ASS’T ENG., N. Y. C. & H. R. R.
E. & F. N. SPON,
NEW YORK: 44 MURRAY STREET.
LONDON: 16 CHARING CROSS.
1882.
Copyright, 1882, by Arthur S. C. Wurtele.
INTRODUCTION.
During the preparation of this investigation of StandardMeasures a large number of authorities were examined,including the following: Kelly’s “UniversalCambist,” Maunder’s “Weights and Measures,” “EncyclopædiaBritannica,” “Chambers’ Encyclopædia,” Williams’“Geodesy,” Hymer’s works, “Smithsonian Reports,” “CoastSurvey Reports,” Herschel’s “Astronomy,” etc. The onlyconcise and clear statement I found was J. E. Hilgard’sreport to the Coast Survey on standards in 1876, which Iwas gratified to find coincides with my deductions.
Arthur S. C. Wurtele.
Albany, November 26, 1881.
STANDARD MEASURES.
A standard measure of length at first sight appears tobe very simple—merely a bar of metal of any length, accordingto the unit of any country; and comparisons ofdifferent standards do not seem to present any difficulty.But on looking further into the thing, we find that standardsare referred to some natural invariable length, andwe are at once confronted with a mass of scientific reductionsgiving different values to the same thing, accordingto successively improved means of observation. We find,also, that comparisons of one standard with another differ,as given by reductions carried to great apparent exactness.
Every author appears to assume the right of using hisown judgment as to what reduction is to be consideredthe most exact, and the result is a very confusing differencein apparently exact figures, with nothing to showhow these differences arise.
I have endeavored to indicate what may be the causeof this confusion by giving the figures of actually observedcomparisons and reductions; in a manner, the rootsof the figures used as statements of length.
Sir Joseph Whitworth gives 1/40000 of an inch as thesmallest length that can be measured with certainty, withan ultimate possibility of 1/1000000 of an inch; but imperceptiblevariations of temperature affect these infinitesimal[4]lengths to such an extent that he believes the limitcan only be reached at a standard temperature of 85° F.,to avoid the effect of heat of the body.
It appears to me that comparisons should be made ofdouble yards and mètres with the old French toise, as thelimit of exactness would be thereby doubled.
Another great defect in statements of relative values isthe omission of necessary facts—the material of whichthe bars or standards are made, the temperature at whichcomparison was made, and the standard temperatures usedas to the final reduction, with the coefficient of expansionadopted.
Again, bars of different metals appear in time to sensiblychange their relative length.