COMPARISON OF UNITED STATES AND FRENCH STANDARDS.

In 1817 Mr. Hassler examined the French standards in America, for the Coast Survey, using the Troughton bronze standard scale, which is identical with Sir George Schuckburg’s standard, as the reference, with the following results, all being reduced to temperature of 32° F.

Original Iron Mètre,179939·381022708inches.
Lenoir Iron Mètre,Coast Survey39·37972015“
“ Brass ““39·380247972“
“ “ “Eng. Dept.39·38052739“
Canivet Iron Toise,176876·74334472“
Lenoir “ “76·74192710“

In 1814 Troughton had compared with his own scale in London two of the above.

Lenoir Iron Mètre,C. S.39·3802506inches.
“ Brass ““39·3803333“

In 1832, under resolution of Congress, Hassler again compared the French standards in the United States, using as before the Troughton scale, and reducing all to temperature of 32° F. as follows:

OriginalIron Mètre,179939·3808643inches.
Lenoir““ C. S.39·3799120“
“Brass MètreC. S.39·380447“
““Eng. Dept.39·3801714“
“““ in 182939·3807095“
Fortin“State Dept.39·3796084“
“Treas. “39·3795983“
Iron Mètre“ “39·3807827“
Gilbert“Univ. of Virg.39·365408“
Platinum Mètre39·3803278“
“(Nicollet)39·380511“
CanivetIron Toise,176876·74290511“
Lenoir“179976·74047599“

From the mean of his comparisons between the United States brass Troughton standard yard and the authentic French standard mètres used by the Coast Survey, Hassler, in 1832, deduced the value of the mètre at 39·3809172 inches, at 32° F., and by correction for expansion to United States standard temperature of 62° F., he made the mètre at 32° equal to 39·36850154 inches at 62° F.

The British imperial standard and the United States Troughton standard differ by only 0·000762 inch, which applied to the English reduction of 39·37079, would give 39·36996 as the relative value according to Troughton standard.

The difference between these reductions is probably to be attributed to the use of different rates of expansion, in correcting for standard temperatures, which vary considerably, according to high authority as follows for brass at 1° F.

Whitworth, 18760·00000956= 0·00034416in. per yard.
Borda, 17990·000009913= 0·00035687“
Smeaton, 17500·000010417= 0·00037501“
Hassler0·000010508= 0·0003783“
Ramsden, 17600·000010516= 0·0003786“
Faraday, 18300·00001059= 0·00038124“

And for the bronze of which the British imperial standards are made:

Airy and Sheepshanks0·0000095= 0·000342in. per yard.
Fizeau0·00000975= 0·000351“

The correction at Ramsden’s rate is nearly identical with Hassler’s, and gives 39·3684933; at Whitworth’s rate it would give 39·36962, very nearly the same as deduced from the difference between the British Imperial standard and the United States Troughton standard. The results of Sir Joseph Whitworth were obtained by use of all late improvements for scientific precision, and they must be accepted as most reliable.

It would appear preferable to give comparisons at the same temperature in connection with the corrected result, so that international comparisons of scientific measurements may not be vitiated by accidental variations.