USED FOR INDICATING ALTITUDES. 



with Shuckburgh's scale, was brought to France in 1801 by Pictet. The comparison 

 of it with the standard metre, made by Prony, Legendre, and Mechain, gave, after 

 due reduction of the two standards to their respective normal temperatures, 



1 metre at 32 Fahr. = 39.371 English imperial inches at 62 Fahr. 

 This determination was adopted for all reductions in Kelly's Universal Cambist, and 

 in the French translation of the work, published in Paris in 1823. 



A new comparison was made with great care by Captain H. Kater, in 1818. (See 

 Philos. Trans, for 1818, p. 103.) The standards used were a brass scale metre, by 

 Fortin, terminated with parallel planes (metre d louts), and a bar of platina on which 

 the length of the metre was marked by two very fine lines (metre a traits). Both 

 were compared with Shuckburgh's scale, and a double series of experiments gave as 

 the mean result : 



Brass metre at 32 Fahr. = 39.37076 inches of Shuckburgh's scale at 62 Fahr. 

 Platina metre at 32 Fahr. = 39.37081 " " " " " 



Mean 39.37079 " " " " " 



On this value of the metre are based the reduction tables by Matthieu, published 

 yearly in the Annuaire du Bureau des Longitudes ; and it has come into general 

 use, both in Europe and in this country. 



Captain Kater gives besides, in the same paper, p. 109, note, the value of the 

 metre compared with Bird's Parliamentary standard as being 



1 metre at 32 F. = 39.37062 imp. inches of Bird's Parliamentary standard at 62 F. 

 This value has been adopted by Dove, as being the legal one, in his reduction tables 

 in his work, Maas und Messen, p. 175, &c., and by many German authorities. 



According to Baily's experiments, made in 1835, when engaged in constructing a 

 new standard for the Royal Astronomical Society (Memoirs R. Ast. Soc., Vol. IX.), 

 the value of the metre is (Lee, Collection of Tables and Formula, p. 62) 



1 metre at 32 F. = 39.370092 imperial standard inches at 62 F. 



The original legal standards having been lost in the fire which destroyed, several 

 years ago, the Parliament Houses, an act of Parliament provided for the construc- 

 tion of new ones ; but as the report of the committee having charge of the con- 

 struction of the new British standard has not yet been published, the discussion of 

 the subject must be postponed. 



The value adopted in the following tables, is that determined by Captain Kater, 

 viz. 1 metre = 39.37079 English inches. 



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 between the 27th and 63d inches of the 



D 111 



