408 Prof. Bessel's Remarks on Mr, Hassler's phmfor an 



of metal in particular ; I fear that without this inquiry there 

 must always remain an uncertainty in respect to the compari- 

 sons of standard measures *. 



Among the various copies of the toise, which Mr. Hassler 

 compared with the English scale, that constructed by Lenoir 

 and compared b}!" Messrs. Bouvard and Arrago appears worthy 

 of being accepted as authentic. When both measures are at the 

 temperature of melting ice, this toise measures Te^V^l 92710 

 inches of the scale of Troughton. By the normal tempera- 



ture of both, = 76-74192710 I^^'StS = "^^'^^SSe English 

 inches. 



As the meter is = 4'43'296 lines of the toise [Base Metriquey 

 torn. iii. page 433), the proportion between the English and 

 French feet, according to Mr. Hassler, will be by the 



™"*^^' = fiS"^^ = 1-0657063, 



toise = ^5^' =1-0657411. 



According to Kater's comparison it is = r0657652. 



It appears then, that the different copies of the meter do 

 not always agree together. Mr. Hassler deduced from several 

 comparisons the value of the meter in parts of the toise, but 

 this I consider is not allowable ; for the ratio between the two 

 is determined by a law, by which the meter has received its 

 true definition ; and the earlier one, that it shall be the ten- 

 millionth part of the earth's quadrant, was lost. If certain 

 copies of these measures do not agree together, it shows only 

 that the law is not exactly fulfilled by them; and as it is much 

 more difficult to transfer to another metallic bar 443,296 lines 

 of the toise than the whole length of the toise, the compari- 

 son of the meter is a circuitous and unprofitable way, as long 

 as the toise itself is yet obtainable as easily as it was at the 

 time of the construction of the meter. 



The apparatus which Mr. Hassler had constructed for the 

 measurement of the base line, differs essentially from all that 

 are known to me; therefore I will describe it somewhat more 

 particularly. The ends of the bars are not planes, but cut out, 



so that viewed from above they present the form 3 ; over this 



middle excavation the hair of the spider's web is stretched, 

 which therefore indicates the end of the bar ; over each of the 



* Copies of the meter have been made of platinum, but it will be ob- 

 vious from these remarks of Bessel, that it is by no means a fit substance 

 for such purposes, inasmuch as it is both difficult to work and to free from 

 adventitious substances. 



ends 



