THE NEW NATIONAL STAND AED OF LENGTH, AND ITS PEINCIPAL COPIES. 681 
Ancient Bars. 
d. 
Henry VII., by comparison with Brass 2 — 1041'34 
Elizabeth, by comparison with Brass 2 — 285‘93 
Excheq., by comparison with Brass 2 — 156 '01 
Tower, by comparison with Brass 2 + 53'27 
Anonymous, by comparison with Brass 2 + 49 ’43 
Mr. SHEEPSHAJfKS usually investigated the “ probable error ” of every result. It has 
appeared to me unnecessary to record them here. They may be understood to range, 
in general, a little above or a httle below 0‘^T, when line-divisions on firm bars were 
compared. 
It will be convenient, in estimating the import of the various numbers given above, 
that the reader should remember the following values : — 
l'^-00 = 0'“"000036 nearly — one-millionth part of the yard-measure. 
I '^•00= Expansion of 36 inches of Bronze for 0°T0 FAiiEEisriiEiT. 
= Expansion of 36 inches of Iron for 0°T7 Fahrenheit. 
For accurate reduction, the following thermometric expansions of 36 inches for 
1° Fahrenheit are to be used : — 
d. in. 
Bronze 
. . 9-507 = 0-000341 
Brass 
. . 9-580-0-000344 
Copper 
. . 8-764-0-000314 
Wrought Iron . 
. . 6-153 = 0-000220 
Cast Iron 
. . 5-527-0-000198 
Cast Steel . . . . 
, . . 5-777-0-000207 
In the statements of results of comparison, it is always supposed that both bars are at 
the temperature 62° Fahrenheit, unless a temperature is stated. 
Between 1855, March 15 and April 3, Mr. Sheepshanks made three careful series of 
observations for ascertaining the effect of flexure on the measure of a bar. Bronze D 
was compared with Bronze 28, the circumstances of Bronze D being varied as follows : — 
1st. Bronze D was supported on block-and-stirrup, the points of support being those 
indicated by theory : 2nd. Bronze D was supported in the middle, a trifling prepon- 
derance being given to one end in order to prevent oscillation : 3rd. Bronze D was sup- 
ported by block-and-stirrup at the extreme ends. The position of Bronze 28 was not 
varied. The results for the excess of Bronze D above Bronze 28 were — 
d. 
1st series, by 96 observations -|-3‘01 
2nd series, by 72 observations -1-3-03 
3rd series, by 72 observations +3’06 
It is sufficiently clear that the effect of flexure is insensible. 
