new standards of weights and measures. 41 



To determine this distance I employed the following 

 method : 



Two bars of brass were prepared, three quarters of an inch 

 square and rather less than 18 inches long. They were ter- 

 minated by planes at right angles to their length ; and upon 

 the upper face of each bar, very near to the end, a fine trans- 

 verse line was drawn ; the other ends of the bars being then 

 placed in contact and kept so by springs, the distance between 

 the lines was taken by means of two micrometer microscopes 

 fixed to a bar of wood and referred to Sir G. Shuckburgh's 

 standard scale, which scale, it has already been remarked, 

 does not sensibly differ from the imperial standard yard. 



The distance between the lines was found by numerous 

 comparisons to be 919 divisions of the micrometer less than 

 the standard yard, each division of the micrometer being 



equal to — ^ of an inch. 

 ^ 23363 



The brass bars were then placed upon the standard to be 

 examined, their marked ends being next each other, and 

 their opposite extremities kept in contact with the steel faces 

 by a spring introduced between the bars, a part below the 

 surface being cut away for that purpose. The distance 

 between the lines was then measured by the micrometer 

 microscope, which distance, had the standard been perfectly 

 correct, would have been equal to what the distance of the 

 lines in the former position of the bars wanted of s^ inches. 



Standard Yard, No. 1. 



The distance between the lines upon the brass bars was 

 found by the mean of six measurements to be 918,2 divisions 

 Df the micrometer, which differs so little from 919 divisions, 



MDCCCXXVI. G 



