OF THE UNITED STATES. 256 



inometre, le metre en cuivre serait plus court que I'eialou 

 en I'er (le nos arcliives de Ti^ine iIc uiilliinetre. 



5. An iron toise standai cled In Lenoir, No. 18 of the cata- 

 logue of instruments. It is an inch and three quarters broad, 

 and one third of an inch thick. The comparison of it by 

 Messrs. Aira2;o and Houvard, made at the same time witli 

 tiiat of the metre al)0\ e. says that it was Ibuntl exactly equal 

 to the toise from Peru in the archives of the observatory. 



fi. One iron metie standarded l)y Lenoir in Paris, but not 

 compared at the observatory of Paris ; l)cin2; No. 18 of tlie 

 catalogue. It is exactly of the same breadth and thickness 

 as the metres of the Committee. 



7. An iron bar, similar to the metre just mentioned, and 

 intended to l)e !)rought to the metre length, in the course of 

 these operations. 



8. The brass standard scale, No. 13 of the catalogue, by 

 Mr. Troughton. It contains 82 inches, divided into tenths, 

 upon a strip of silver extending over its whole length. It is 

 three inches broad, and half an inch in thickness. It bears 

 the arms of the United States, and tlie name, Troughton^ 

 London, 18 1 3. 



To it belongs an ap|)aratus for coiriparing measures by 

 two compound microscopes, sliding on a rule and |)laced pa- 

 rallel to the scale of the same breadth and thickness. One 

 of the microscopes has two fixed wires crossing under 30°, 

 the other a micrometer witli similar wires, pointing out dis- 

 titKtly the ten tliousandth part of an inch. This apparatus 

 has been described in Nicliolson's Journal, and other works. 

 A proi)er apparatus, witli a Hindley's tracing tool, was add- 

 ed, to whicii tlie miciometer microscope is adapted, for the 

 purpose of constructing other scales from this. 



The scale was divided with that extreme care and accuracy 

 for whch Mr. Troughton is so justly |)raisfd. It contains the 

 douliU* length of the principal part of his scale, oC which an 

 account has been given in Sir (leorge Sbuekburgh Kvclyn's 

 paper referred to above. Mr. Troughton tirst compared the 



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