280 PROCEEDINGS OF THE AMERICAN ACADEMY 



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ing the expansion of the platinum-iridium, of which the meters are 

 formed. 



" XIV. The prototype shall be submitted to the best possible pro- 

 cess for the determination of the absolute coefficient of expansion of 

 the whole meters. These measures shall be made separately, at least 

 at five different temperatures comprised between 0° and 40° C." 



" XVII. The comparisons shall be made by immersing the new 

 standards in a liquid and in air, but with the reservation that the 

 standard of the Archives shall not be immersed in any liquid until the 

 close of the operations. 



" XVIII. The tracing of the line-meters, and their first comparison 

 with the ' Metre des Archives,' shall be effected by the process of M. 

 Fizeau." 



In order to gain a clear understanding of what has been accom- 

 plished in accordance with these resolutions, it is necessary to distin- 

 guish between the operations of the French section of the Commission 

 and those of the International Bureau. The construction of the proto- 

 types from the " Metre des Archives " was naturally committed to the 

 French section, the primary standard being the property of the French 

 government, the responsible authority for its preservation in a state of 

 perfect integrity. 



The prototypes thus prepared, after delivery to the International 

 Commission, and after their formal acceptance by the Commission, are 

 to be subjected to the various tests provided for by the articles of the 

 convention. Finally, either one of these prototypes, or, perhaps, the 

 mean of two or three of them, will be officially declared to be the true 

 and final base of reference in all measurements of linear extension. 



The International Bureau is now prepared for its share of the work. 

 The buildings are completed, the instruments of comparison are in 

 position, and nearly all of the provisional investigations required have 

 been completed. The present delay must be charged to the unfortu- 

 nate dead-lock between the Commission and the French section, the 

 Commission refusing to accept the prototypes prepared by M. Tresca, 

 mainly on the ground that the material of which the standards are 

 made is not, in its present condition, a pure alloy of platinum and irid- 

 ium, but that it contains, as is asserted, nearly two per cent of iron. 



The International Bureau at the present time has no standards 

 which have been compared directly with the "Metre des Archives." 

 It has three provisional meters, all of which have been indirectly com- 

 pared with the primary standard. It has a meter made by Repsold, 

 one made by Hermann and Blister, of Berne, Switzerland, and one 



