456 COMPARISON OF THE VARIOUS MEASURES OF LENGTH 



putations, would hardly be justified. For the present, therefore, it seems best not 

 to introduce here this new value, which, after all, may not be a final one. 



It may not be out of place to remark that Schumacher, in the first edition of his 

 Sammlung von Hulfstafeln, used the value 1 metre = 39.3827 English inches, as 

 given in the Base du Systeme Metrique ; but this number, which expresses the rela- 

 tion of both standards when at the freezing point, becomes 39.37079 when they are 

 respectively reduced to their normal temperatures. Schumacher's tables, therefore, 

 must be corrected accordingly. 



4. The actual standard of length of the United States is a brass scale of eighty- 

 two inches in length, prepared for the Coast Survey of the United States, by Trough- 

 ton of London, meant to be identical with the English Imperial Standard, and depos- 

 ited in the office of weights and measures. The temperature at which it is a standard 

 is 62 Fahrenheit, and the yard measure is traced between the 27th and 63d inches 

 of the 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 Fortin 

 verified by Arago, and found to be I^-Q 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 " " u 



3. Platina metre of Fortin = 39.3804194 " " " 



Or, correcting for expansion, and reducing them to 'their respective standard tern 

 peratures : 



1. Iron metre of Tralles at 32 F. = 39.36850 \ English inches of the 



2. Iron metre of Lenoir at 32 F. = 39.36754 V Troughton scale of 



3. Platina metre of Fortin at 32 F. 39.36789 J 82 inches at 62 F. 



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. ; 

 which reduced by Prof. A. Bache, his successor, by means of the coefficient of ex- 

 pansion by heat used by Hassler, became 



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



This scale and its metric equivalent was regarded as the United States standard 

 from which copies were to be made. 



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

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

 E 10 



