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. [Illustration] 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 Standard Measures a large number of authorities were examined, including the following: Kelly’s “Universal Cambist,” Maunder’s “Weights and Measures,” “Encyclopædia Britannica,” “Chambers’ Encyclopædia,” Williams’ “Geodesy,” Hymer’s works, “Smithsonian Reports,” “Coast Survey Reports,” Herschel’s “Astronomy,” etc. The only concise and clear statement I found was J. E. Hilgard’s report to the Coast Survey on standards in 1876, which I was 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 to be very simple--merely a bar of metal of any length, according to the unit of any country; and comparisons of different standards do not seem to present any difficulty. But on looking further into the thing, we find that standards are referred to some natural invariable length, and we are at once confronted with a mass of scientific reductions giving different values to the same thing, according to 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 his own judgment as to what reduction is to be considered the most exact, and the result is a very confusing difference in apparently exact figures, with nothing to show how these differences arise. I have endeavored to indicate what may be the cause of this confusion by giving the figures of actually observed comparisons and reductions; in a manner, the roots of the figures used as statements of length. Sir Joseph Whitworth gives 1/40000 of an inch as the smallest length that can be measured with certainty, with an ultimate possibility of 1/1000000 of an inch; but imperceptible variations of temperature affect these infinitesimal lengths to such an extent that he believes the limit can only be reached at a standard temperature of 85° F., to avoid the effect of heat of the body.