THE Jv'EW NATIONAL STANDAED OF LENGTH, AND ITS PEINCIPAL COPIES. 6G9 
From these were obtained, for 1° Fahrenheit, — 
Absolute expansion of 36 inches of Bronze=0’09507 
Absolute expansion of 36 inches of Brass =0'09601 ; 
and by combining the absolute expansion of Bronze with the excess of expansion of 
Bronze above Iron-, 
Absolute expansion of 36 inches of Iron=0‘'‘06189, 
In the spring of 1850, from February to April, Mr. Sheepshanks determined the 
scale of the two thermometers L and E, by comparison with five original thermometers 
of the A series; and in 1849 and 1850 he compared I and s with two of the same series. 
From this time, I conceive, every observation possesses extraordinary value. 
In the summer of 1850, seventeen bronze bars and two copper bars were compared 
■wnth Bronze 12. The excesses of their lengths over that of Bronze 12 were as follows : — 
r. 
Bronze 2 
-0-0252 
6 
-fO-0042 
'rr 
i 
—0-0272 
8 
-0-0018 
18 
-0-0347 
19 
+ 0-0014 
20 
-0-0146 
21 
-0-0034 
22 
+0-0033 
23 
-0-0054 
24 
+0-0107 
25 
+ 0-0840 
26 
+0-0379 
27 
-0-0010 
28 
-0-0155 
29 
+ 0-0364 
30 
+ 0-0386 
Donkin’s Copper 
+ 0-0397 
Mat’s Alloy (32 copper, 1 tin) -j- 0-0547 
In the course of these observations, Mr. Sheepshanks saw reason for abandoning 
Bronze 12 as Basis, and adopting Bronze 28 in its stead. He remarked that the 
length of Bronze 28 (=Bronze 12 — 0''-0155 = 36'" '000048 — 0‘"”000056 = 35'" '999992) 
was as nearly as possible that of the Imperial Standard, that the bar floated evenly in the 
quicksilver, and that it was nicely divided. Bronze 12 was not nicely divided, and did not 
float evenly; and one of its gold dots was much tarnished while the other was quite 
bright ; and the tarnished dot was much disfigured by a mercurial stain. Another con- 
sideration, which afterwards led to extensive series of observations, was the following. 
MDCCCLVII. 4 s 
