THE ART OF WiaGIIlNC AND MEASURING. 



G27 



Society's troy pound \v;ks :\.\) orains lighter than tlie Imperial standard 

 of 1758 ; whence 



K. S. trov i»()nnd -|- 3.9 grains — Standard of 1758 (10) 



but 



standard of 1858 := Excli. (8 ounces + 4 ounces) -f li grains (11) 



and therefore 



R. S. troy pound = Ex(di, (8 ounces -}- 4 ounces) — 2§ grains (^12) 



Considering the indetiniteness of the data respecting the weighings 

 made in 1820, equations (9) and (12) agree fairly well, but equation (5) 

 is very discordant, as are also equations (7) and (8). All the evidence 

 seems to point to an error of about li grains in equation (5) ; and if 

 instead of (5) sve write 



R. S. Troy pound — Excli. (8 ounces + 4 ounces) — 2 grains (5') 



(7) will become 



Exch. (8 ounces + 4 ounces) = Mint (8 ounces + 4 ounces) — | grain (7') 



and then all the equations will be reasonably accordant. 



Note C. [Subsequently added.] 



Assistant O. H. Tittmann, of the U. S. Coast and Geodetic Survey, 

 in charge of weights and measures, has recently shown that the dis- 

 crepancies in the values assigned to the meter in terms of the yard 

 depend mainly upon errors either in the assumed lengths or in the 

 assumed coetiicients of expansion of the standards employed.* By a 

 skillful use of the data published by the various observers, combined 

 with the known coefficient of (expansion of the iron committee meter, 

 "CM," of the U. S. Coast and (Tcodetic Survey, he has succeeded in 

 determining the absohite expansions of the standards in question, and 

 by means of these expansions he has referred all the observations to 

 the said committee meter and to the present British Imperial yard. 

 From the data thus reduced to a common standard he has obtained 

 the very consistent results given in the fonrth column of the following 

 table. The values in the third column are those published by the ob- 

 servers themselves, and it is now evident that they really depend upon 

 several different British and metric units. As there is no means of re- 

 ferring the standard used by Prof. \V. A. Rogers to the committee meter, 

 his result could not be included in the table. 



LENGTH OF THE METER EXPRESSED IN ENGLISH INCHES. 



* See 73 and 74. 



