232 Translation from the Astronomical Jour, of Hamburgh. 



a small chemical difference may not have a remarkable influ- 

 ence upon it : this investigation is more easy than that of the 

 absolute expansion itself It can be known only after a pre- 

 vious experiment of this kind, whether the results of two ob- 

 servers must agree in the same metal ; or if it is really neces- 

 sary to determine the expansion for each piece of metal in 

 particular : I fear that without this enquiry there must always 

 remain an uncertainty in respect to the comparisons of stan- 

 dard measures.* 



Among the various copies of the toise, which Mr. H. com- 

 pared to the English scale, that constructed by Lenoir and 

 compared by Messrs. Bouvard and Arrago, appears worthy 

 of being accepted as authentic. When both measures are 

 at the temperature of melting ice, this toise measures 

 76,74192710 inches of the scale of Troughton. By the 

 normal temperature of both, 



1,0002036843 _ ,. , . , 



= 76,74192710 ^ 0003152709 ^'^^''^^^^^ English mches. 



As the meter is =443,296 lines of the toise, (Base metrique, 

 tome iii, page 433,) the proportion between the English and 

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



39,36861 



'"^^^••'=4ii;296-12=^'0^^^^^^' 



76,73336 

 toise, = ^2 — =1,0656411. 



According to Kater's comparison, it is =1,06576411. 



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

 not always agree together. Mr. H. 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 re- 

 ceived 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 

 shews 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 comparison of the meter is a circuitous and unprofitable 



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

 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. 



