COMPARISONS OF UNITED STATES AND ENGLISH STANDARDS.

In 1832, under resolution of Congress, Mr. Hassler compared the different standard yards in America, with the following results, using the yard between the twenty-seventh and sixty-third inches on the scale made of bronze by Troughton, of London, for the United States Coast Survey, as the reference, that being identical with Sir George Schuckburg’s standard:

Troughton Scale, mid. yard36·0000000inches.
“ “ between platinum points35·9989758“
Jones yard in State Department35·9990285“
Iron yard in Engineer Department35·9987760“
Brass yard, Albany, Sec. of State36·0002465“
Gilbert yard, University of Virginia35·9952318“

In 1856 the Troughton standard bronze scale was compared with the bronze standard yard No. 11, which was sent over by Airy as a copy of the English imperial standard, as restored after destruction of the original standard by fire in 1834, and the United States standard was found to be longer by 0·00085 inch.

Later comparisons by J. E. Hilgard, of the Coast Survey, of the bronze standard No. 11 with the imperial standard yard, at the British Standards Office, gave No. 11 as 0·000088 shorter than the imperial standard.

Hassler’s reduction of the mètre, as deduced by Beach at 62° F., 39·36850154, compared with the English reduction of the mètre, 39·37079 inches, gives an excess to the United States Standard of 0·002029 inch.

The following reductions have been given for the United States yard in English inches:

Report of Sec. of Treas., 185736·00087= 1·00002416
Chambers’ Encyclopædia, 187236·00087
“ “ “36·0020892= 1·0000580334
Trautwine36·0020894= 1·000058038
Mathewson, U. S. surveyor36·00208944= 1·00005804
Hassler and Beach36·002092= 1·00005811
J. E. Hilgard, Coast Survey36·00076= 1·000021

To Mr. Hassler’s reduction the name of United States inch has been applied; but his reduction is not correct, as he used a rate of expansion for brass deduced by himself of 0·0003783 inch in one yard for 1° F., and later experiments show that the smaller rate of 0·000342, deduced by Airy, is more correct.

By correcting Hassler’s reduction with the later rate of expansion, J. E. Hilgard shows that the difference would be very small, or only 36·0002286 = 1·00000635, or about ⅖ of an inch in a mile.

In Coast Survey report for 1876, J. E. Hilgard calls attention to another difficulty in the matter of extreme accuracy, in the uncertainty with regard to the permanence in the length of a bar, and states that the bronze standard bar No. 11 and the Low Moor iron standard bar No. 57, presented to the United States by Great Britain, are found to have changed their relative length by 0·00025 inch in 25 years; the bronze bar being now relatively shorter by that amount. This subject, he states, is undergoing further investigation.