accurate Survey of the United States of America. 407 



the length of the meter was determmed to be 39-381022708 

 inches of the scale, which, as the standard temperature of the 

 English measure is 62° Fahr., gives the length of the meter in 

 English inches 



= ''''T .T1 = 39-36861 English inches. 

 1-0003152709 ^ 



The two other copies of meters give less (O'OOl inch) ; but these 

 were compared both with the scale of Troughton in Ame- 

 rica and that which this artist himself uses in London, and 

 had upon both very nearly the same length ; whence it may 

 be concluded, that both English scales agreed very nearly. 

 Thus according to Mr. Hassler's comparison the meter is 

 39"36861 English inches: according to the comparison of two 

 other copies by Kater = 39*'57079. According to vol. iii. of 

 Base du Sijsteme Metrique, page 469, the meter of platinum 

 was = 39-382755; that of iron"= 39-382649: both measured 

 upon the brass scale of Mr. Pictet, reduced to the temperature 

 of melting ice; at a mean = 39-3827, which, according to 

 Borda's expansion for brass (0-001783, by which the experi- 

 ments made in Paris were reduced to the point of melting ice, 

 from a temperature = 12°-75 Centigrade, at which they were 

 made) gives 39-37100." The two last comparisons agree very 

 nearly, and their difference lies entirely within the limits of the 

 uncertainty of thermometrical influence. The authentic meter 

 of Mr. Hassler appears, however, really to be shorter, though 

 it could be brought nearer to the others, by adopting other 

 proportions for the expansion of metals*. This, however, ap- 

 pears not to be allowable, when the results of different com- 

 parisons are to be collected ; for the determination of the ex- 

 pansion is as important as the comparison itself; therefore, 

 each observer nmst remain answerable for that one which he 

 adopts. I think it should be inquired whether two metals of 

 the same chemical composition have the same proportion of 

 expansion ; or if a small chemical difference may not have a 

 remarkable influence upon it; this investigation is more easy 

 than that of the absolute expansion itself. It can be known only 

 after a previous experiment of this kind, whether the results 

 of tlie two observers must agree in the same metal ; or whether 

 it is really necessary to determine the expansion of each piece 



• The meter used by Mr. llasslerin his comparisons, and wliich the 

 Chevalier Hessel suspects to have been too short, was an (mgiiuil issued by 

 the French commhsinn, and is therefore far more aiitlientic than the copies 

 used by Kater. We are happy, however, to be able to state, that Mr. Hass- 

 ler has recently been engaj^ed at Wasliington in further comparisons, and 

 will probably make his results public in a short time. They arc said fully 

 to confirm his former experinients. 



of 



