L. Bell — Absolute Wave-length of Light. 277 



The yard and meter C. S. has its graduations on silver pings 

 in a brass bar. The yard was compared directly with the Im- 

 perial Yard, in 1880, and the standard was then sent to Bretenil 

 where it was compared with the International Meter by Dr. 

 Pernet. 



There were thus two completely independent sources from 

 which the relation of R 2 to the Metre des Archives could be 

 obtained. The results derived by very elaborate comparisons 

 with each of these were as follows : 



l r ° m Ja 5"l' = i !'f U16-67C. 

 From Co. R 2 — A = + 1-1/j \ 



Where A is the Metre des Archives. . In addition to the 

 very close agreement of the above, further evidence was ob- 

 tained by deriving the relation between the yard and meter 

 from R 2 , the yard R 2 having been exactly determined by com- 

 parisons with C. S.. and with " Bronze 11," one of the primary 

 copies of the Imperial Yard, which had been recompared with 

 that standard in 1878. 



From the comparisons of S x and S 2 made in 1885 the follow- 

 ing value of those standards were deduced : 



S\ + 0-98,u = |A , and 

 S a 2 + 0-2// = |A . Hence 

 S a 2 = S a a + 0*78>u, and for the first decimetei-s 



were found the relations : 



Dm^ + 0-05/; = T VA Wh 

 Dm^*, - 0-0 l/i = -jLA vv nence ' 

 Dm 1 S a 2 = Dm 1 S a 1 + 0-06/j. 



On these equations were based the results embodied in my 

 former paper. In the latter part of May, 1887, these standards 

 were very carefully compared with each other and with a 

 speculum metal bar graduated by Prof. Rowland, as I desired 

 to take one or more of the standards to Berlin during the sum- 

 mer in order to get a comparison with the standard used by 

 Muller and Kempf . 



The results of this examination were of a somewhat startling 

 character, as follows : 



S%=S a 1 + 1-2 /a, direct 

 ■ S a 2 = S a x -f l'lyw, through the Rowland bar 

 designated R B . Also, 



Dm 1 S a 2 = Dm 1 S a 1 + VI /u, through R B 



In 1885 Rogers had found for the relation between the two 

 decimeters of each bar : 



Dm„8 a 1 = Dm^ 1 , — 0-56/.< 

 DmjS a 2 = Dm 2 S% + 0-46,u 



