138 Further Experiments on the [Marcu, 
Abstract of the results of the foregoing experiments on the expansion of 
“ the Standard 10 feet Bar of Iron. 
a a ES, 
No. of | Range of |Divisionsof} Total expansion Plaga ie hig Aaa tea 
the se-|Temperature |the micro-|in decimal parts of 
length at 32° is} mean in 
ries. Farh. meter. a foot. 1, 1,000000, Hallion the 
t+) 
lr 136,0 2213 .0090980 1.001204 — 14 
27 134,6 2171 -0089253 1.001194 — 24 
St 140,6 2296 -0094392 1.001208 — 10 
3 r 138,9 2288 -0094064 1.001219 + 1 
St 131,5 2218? .0091185 1.001248 + 30 
St 140,7 2370 ? .0097435 1.001246 + 28 
ar 138,7 2283 .0093858 1.001218 0 
Sf 139,2 2306 .0094804 1.001226 + 8 
57 139,2 2298 .0094475 1.001222 + 4 
if 139,5 2283 .0093858 1.001211 — 7 
6r 139,1 2288 .0094064 1.001217 — il 
of 139,7 2288 -0094064 1.001212 — 6 
77 139,7 2293 -0094269 | 1.001214 — 4 
Mean of the whole, 1.001218 
The mean of these experiments is 1.001218, but if two of the series 
(doubtful because they depend on single observations), be struck out, 
the dilatation will appear to be 1.001213, and the greatest deviation 
hardly amounts to the one hundred-thousandth part, while the general 
accordance is much within these limits. The mean of the former ex- 
periments upon an iron rod of 25 feet in length was 1.001256, deter- 
mined by a single heating, and therefore liable to some uncertainty : 
that of another wrought iron bar to be noticed presently, was 1.001216, 
which agrees so closely with the above, as well as with the results of 
Smeaton and Lavoisier, that I am inclined to think there is not so much 
variation due to the quality of the metal as has sometimes been sup- 
posed, and that 1.001215 may be safely employed on all occasions as 
the constant of expansion for wrought iron. 
Il.— Expansions of Gold, Silver, and Copper. 
Having concluded the experiments upon the standard bar of the 
trigonometrical survey, it occurred to me as very desirable to make 
use of the microscopes, while fixed, to lay off a duplicate of the bar for 
deposit in my own office. "When this had been done, it followed that 
the constant of expansion might likewise be determined with ease for 
the new bar by a repetition of the same process ;—and further that we 
might arrange alongside of the iron bar such other metals as were 
readily procurable in the mint of the desired dimensions. 
Captain Wilcox kindly undertook to assist me in this new series, 
which was conducted in every respect with the same attention to mi- 
