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. yard 36·0000000 inches.
“ “ between platinum points 35·9989758 “
Jones yard in State Department 35·9990285 “
Iron yard in Engineer Department 35·9987760 “
Brass yard, Albany, Sec. of State 36·0002465 “
Gilbert yard, University of Virginia 35·9952318 “
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., 1857 36·00087 = 1·00002416
Chambers’ Encyclopædia, 1872 36·00087
“ “ “ 36·0020892 = 1·0000580334
Trautwine 36·0020894 = 1·000058038
Mathewson, U. S. surveyor 36·00208944 = 1·00005804
Hassler and Beach 36·002092 = 1·00005811
J. E. Hilgard, Coast Survey 36·00076 = 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.