COMPARISON OF THE VARIOUS MEASURES OF LENGTH 



scale. (See Report on the Construction and Distribution of Weights and Measures, 

 by Prof. A. D. Bache, 1857.) 



Hassler, first Superintendent of the United States Coast Survey, made an elaborate 

 comparison of eleven different standard metres with the brass scale of eighty-two 

 inches, by Troughton. Three of the standard metres, certified to be correct by high 

 authorities, seem to deserve especial confidence : 1. An iron metre, presented to 

 Mr. Hassler by Tralles, which was one of the three that Tralles had made by Lenoir 

 at the same time with those distributed to the committee on the weights and measures. 

 2. Another metre of iron, also by Lenoir, verified by Bouvard and Arago, and de- 

 clared by them to be identical with the original. 3. A platina standard by Fbrtin, 

 verified by Arago, and found to be T ^ of a millimetre too long, for which error 

 allowance was made. Their comparison with the Troughton scale at the tempera- 

 ture of the freezing point gave : 



1. Iron metre of Tralles = 39.3809171 inches of the Troughton scale. 



2. Iron metre of Lenoir = 39.3799487 



3. Platina metre of Fortin = 39.3804194 



Or, correcting for expansion, and reducing them to their respective standard temper- 

 atures : 



1. Iron metre of Tralles at 32 F. = 39.36850)^ .... , . . ^ , 



^^r A ( English inches of the Trough- 



2. Iron metre of Lenoir at 32 F. = 39.36754 > . * 



o^o -r. or. o^-,on 1 ton sca ^ e f 82 inches at 62 F. 



3. Platina metre of Fortm at 32 F. = 39.36789 ) 



Hassler, in his Report to Congress on Weights and Measures, in 1832, adopts the 

 first value, viz. : 



1 metre at 32 F. = 39.3809171 inches of the Troughton scale at 32 F ; 

 and the Troughton scale was declared the United States standard, from which copies 

 were to be made. 



This value materially differs from those given by other careful comparisons, while, 

 on the other hand, the close accordance of the numbers corresponding to the various 

 standard metres proves the accuracy of Hassler's method and comparison. It is, 

 therefore, difficult not to ascribe, with Baily, this discrepancy to some inaccuracy in 

 the length of the Troughton scale of 82 inches. But as that scale has been declared I 

 the standard of length of the United States, it seems better to call it, as is done in the 

 Coast Survey Reports, the American yard, and its subdivisions the American foot 

 and inch, and to consider it as a new standard, similar to, but not identical with, the 

 English imperial standard. The value of the metre expressed in American standard 

 inches is given in the Coast Survey Report for 1853, as 



1 metre at 32 F. = 39.36850535 United States standard inches at 62 F. 



We learn from the Report on Weights and Measures, by Prof. A. D. Bache, 1857, 

 p. 18, that two copies of the new British standards, now in progress of construction, 

 viz. a bronze standard, No. 11, and a malleable iron standard, No. 57, have been pre- 

 sented by the British government to the United States. A series of careful compari- 

 sons, made in 1856, by Mr. Saxton, under the direction of Prof. A. D. Bache, of the 

 British bronze standard, No. 11, with the Troughton scale of eighty-two inches, 

 showed that the British bronze standard yard is shorter than the American yard by 

 0.00087 inch. 



D 112 



