294 PROCEEDINGS OF THE AMERICAN ACADEMY 



very irregular, and that the normal action under a given change of 

 temperature could be obtained only by maintaining a constant temper- 

 ature for about twelve hours. Fortunately, a portion of the compari- 

 sons with the Imperial Yard were made under the required conditions, 

 at the nearly constant temperature of 57° Fahr. When it became 

 apparent that the transfer at 62° Fahr. from the steel bar to a bronze 

 bar identical in form and construction with R^ could not be made 

 vpith the required exactness, it was decided to make the required 

 transfers under conditions as nearly as possible the same as those 

 under which the comparisons had been made at London. After main- 

 taining the nearly constant temperature of 57° for about twenty-four 

 hours, this transfer was made to a bronze bar designated R^. After 

 applying the reduction from 57° to 62°, Professor J. E. Hilgard, now 

 Superintendent of the U. S. Coast Survey, having kindly offered to 

 compare this yard vrith the standard yard known as "Bronze 11," 

 which bears a known relation to the Imperial Yard, bar i?Q was sent 

 to Washington for this comparison. According to the report of Pro- 

 fessor Hilgard, this yard was found to be 24 millionths of an inch 

 longer than " Bronze 11," or 64 millionths of an inch shorter than 

 the Imperial Yard, adopting the relation 



" Bronze 11 " -|- .000088 in. = Imperial Yard. 



It was now possible to make the transfer from R^ to ^2 ^i^h but 

 little regard to the question of temperature, and with a known relation 

 to the Imperial Yard. This transfer was made, January 13, 1881. 

 The yard R.^^ is subdivided into feet, and the first foot is further 

 subdivided into inches. At one end a single line defines the limit 

 of botli the yard and the meter. The other defining line of the 

 meter extends beyond the corresiDonding defining line of the yard 

 3.37 inches. For convenience in measuring this space, the yard is 

 extended to 39 inches, with inch subdivisions. Subsequently the 

 system of graduations upon R^ were transferred to the brass surface 

 of this bar, being traced near the edge. This set of graduations is 

 designated R^. 



IV. The Brass Yard and Meter designated O. S. 



This standard was prepared by the U. S. Coast Survey many years 

 ago, and presented to the Stevens Institute at Hoboken, N. J. By 

 the kindness of President Morton I was permitted, in January, 1880, 

 to take this standard to London in order to obtain a comparison of 



