OF ARTS AND SCIENCES. 287 



est of science, and by the legalization of Bronze No. 1 as the Imperial 

 Standard Yard, with which it had been most carefully compared; but 



I am not aware that it has ever been sanctioned by act of Congress. 



For the metric system, the iron meter mentioned above has always 

 been taken as the standard of reference. It has, however, no legal 

 sanction. Neither in the case of the yard nor of the meter are com- 

 parisons usually made directly with the original standards. 



The Saxton comparator consists of a brass bed-plate having V-shaped 

 ways running the entire length. A slide carrying a microscope slides 

 freely over these ways. A series of brass posts form a part of this 

 bed, through which pass steel screws having conical ends, which have 

 been tempered and polished. There are stops for the yard and for its 

 subdivision into feet, and of one foot into inches. There are also 

 stops for the meter and for its subdivision into decimeters, and of one 

 decimeter into centimeters. By a very ingenious arrangement, the arm 

 attached to the moving microscope plate can be brought into contact 

 with any stop without loss of motion. The end stops for the yard and 

 for the meter were many years ago set to correspond with " Bronze 

 No. 11 " at 58° nearly for the yard, and with the iron meter at 68° 

 nearly. It is understood that the position of these stops with respect 

 to the brass bed have never been changed. The standards which 

 have been distributed since 1856 have been transferred from these dis- 

 tances at the temperatures at which they are standard. The yard in 

 actual use at the Bureau of Weights and Measures, therefore, may be 

 defined to be the distance between two steel stops attached to the bed 

 of the Saxton comparator which corresponds to the length of " Bronze 

 No. 11" at 58° nearly, and the meter may be defined to be the dis- 

 tance between two steel stops of the Saxton compai'ator which corre- 

 sponds to the length of the iron meter corrected for the difference 

 between its length at 32° and at 68° nearly. Recent comparisons 

 indicate that these temperatures should be diminished, by a trifling 

 amount, for the present distances between the stops, both for the yard 

 and for the meter. 



In May, 1878, by the kindness of Prof. J. E. Ililgard, Assistant in 

 Charge of the United States Coast Survey, I was able to secure copies 

 of both the yard and the meter, together with their subdivisions. On 

 .May 14, Dr. Clarke, who has charge of the standards, transferred the 

 yard to a glass bar which I had previously prepared, and on the morn- 

 ing of May 17 the meter with its subdivisions was transferred to the 

 same bar. 



Upon my return to Cambridge, the relative relations between the 



