236 PROCEEDINGS OF THE AMERICAN ACADEMY 



num end-measure meter, deposited in the Archives of Paris, is the only 

 ultimate standard of reference. Since sixteen governments have en- 

 tered into the Convention, which, through the International Commis- 

 sion, has decided that this particular bar at 0° Centigrade shall be the 

 unit to which all measures of extension shall be referred, there is 

 hardly a possibility that a different unit will ever be adopted. Great 

 Britain is the only prominent government that has declined to enter 

 the Convention. The two platinum meters which have hitherto been 

 the standard of reference in that country are, however, no longer 

 adapted to the purposes of exact measurement. Besides, even here 

 the ultimate reference is the Meter of the Archives, through the equa- 

 tion determined by Kater and Arago in 1818. 



The only exception to the entire abandonment of all attempts to 

 refer the meter to a natural unit is the indirect determination by 

 Clarke and others of the length of this unit expressed in the ten-mil- 

 lionth part of a quadrant of the earth's surface. With the highest 

 possible respect for the work which has been done by Colonel Clarke, 

 it does not seem likely that his value of this unit will ever become 

 generally adopted. In the first place, his arc of the meridian does not 

 follow the definition upon which the Meter of the Archives was 

 founded. In the reference to any given unit, the standard of length 

 determined must be ascertained with a greater degree of exactness 

 than that attainable in the comparison of different copies of this stand- 

 ard. It is the experience of the writer that the error involved in 

 the comparison of different meters need not exceed one millionth of a 

 meter. It is not probable that an arc of a meridian of the earth's sur- 

 face extending over 90° of latitude can be measured with sufficient 

 exactness to warrant the assignment of this degree of accuracy to the 

 aliquot part of this distance, which we call a meter. 



In the United States, the particular yard which, previous to 1856, 

 was taken as a standard, is the distance between the 27th and the G3d 

 inch of a scale by Troughton. It has never had other than an indi- 

 rect legal authority. It was never legalized by act of Congress. It 

 was, however, adopted by the Treasury Department. The first stand- 

 ards distributed to the States by the authority and direction of Congress 

 were copies of this particular bar. 



In 1856, "Bronze bar No. 11 " was presented by the British Board 

 of Trade to the United States. It is standard at 61°. 79 Fahrenheit. 

 Since this date, all measures of length which are expressed in terms of 

 the yard have been referred to this particular unit. This change, by 

 whatever authority it was made, was one clearly demanded in the inter- 



