THE NEW NATIONAL STANDAED OF LENGTH, AND ITS PEINCIPAL COPIES. 687 
would seem that the steel and agate formed a galvanic combination, like zinc and copper ; 
and that the air, or its moisture, then acted energetically upon the steel. The steel 
plugs were then withdrawn, and agate plugs were substituted, and no further difficulty 
w'as experienced. 
In the definitive comparisons at Somerset House, the bars were always supported on 
lever-frames, in the manner shoAvn in figures 11 and 12. 
The folloufing is an abstract of the comparisons : — 
Bronze End-bars called No. 45, No. 69, and No. 74 compared with Bronze 28. Ob- 
servations by Mr. W. Simms, jun. and Mr. James Simms. One division=0*'’'‘0000369. 
+ — d. 
No. 69 with No. 74, by 48 observations, exceed Bronze 28 by — 13-66 
+ — 
No. 74 with No. 69, by 48 observations, exceed Bronze 28 by -f-17-67 
Therefore No. 74-|-No. 69 exceed 2 X Bronze 28 by -j-4'^-01. 
+ — 
No. 69 with No. 45, by 48 observations, exceed Bronze 28 by — 1'43 
+ — 
No. 45 with No. 69, by 48 observations, exceed Bronze 28 by + 2-79 
Therefore No. 69-1-No. 45 exceed 2 x Bronze 28 by -j-l‘*-36, 
+ — 
No. 45 ufith No. 74, by 48 observations, exceed Bronze 28 by —14-28 
+ — 
No. 74 ufith No. 45, by 48 obsei-vations, exceed Bronze 28 by -{-13‘37 
Therefore No. 45-1-No. 74 exceed 2 x Bronze 28 by — 0‘’-91. 
Soh-ing the three equations, 
d. 
Bronze End-bar No. 45 = Line-measure Bronze 28 — 1-78 
Bronze End-bar No. 69 = Line-measure Bronze 28-1-3-14 
Bronze End-bar No. 74= Line-measure Bronze 28-1-0-87 
End-bars called Steel 72, Steel 73, and Iron 70 compared with Line-measure Steel B. 
Steel 73 with Steel 72, by 48 observations, exceed Steel B by -1-5-31 
4 * — 
Steel 72 with Steel 73, by 48 observations, exceed Steel B by —3-92 
Therefore Steel 73-1-Steel 72 exceed 2 X Steel B by -|-1^‘39. 
In these comparisons, the temperature is unimportant. 
+ — 
Iron 70 with Steel 72, by 48 observations, exceed Steel B by — 12-71 
+ — 
Steel 72 with Iron 70, by 48 observations, exceed Steel B by fi- 9-10 
Therefore Iron 70-1-Steel 72 exceed 2 x Steel B by — 3‘’-61. 
These comparisons were made at mean temperature 50°-48. But the expansion of 
Iron (36 inches) for 1° FAHEE]srHEiT=6‘^-153 ; that of Steel=5'^-777 : the relative expan- 
sion of Iron therefore = -l-0‘*-376 ; or for ll®-52 Faheenheit= -l-4‘^-35. Hence at 
4 u 2 
