THE XEW JfATIOXAL STAHDAED OF LENGTH, AND ITS PEINCIPAL COPIES. 6G7 
Split-Plug A was then used as a bar of reference with which fourteen bronze bars 
were compared. 
It was also compared directly with the Eoyal Society’s Scale ; but the result of this 
du-ect comparison, 36“ -000485, did not exactly agree with that of the indirect comparison 
through Brass 2. After remarking this discordance, Mr. Sheepshanks adds, “ There was 
another objection to making the spht-plug bar my standard. The construction is not 
mechanically sound ; the ditference from the true yard leaves too much influence to the 
micrometer ; and I have upon it no scale by Avhich I can control the micrometer. 1 
found too that by my better arrangement of the light, the superiority of the split-plug 
was no longer e\ident. So I looked over the values of my bars compared with Split- 
Plug A, and selected Bronze 12 as generating standard to which everything is to be 
referred.” 
After this decision, no farther use was made of the results of comparisons of bars with 
Split-Plug A. The di\ided plugs were removed from A and from another of similar 
construction called Split-Plug B, and they were then fitted with gold plugs and incised 
lines in the same manner as the others, and were called Bronze 39 and Bronze 40. 
In the month of September 1849 Mr. Sheepshanks proceeded to compare Bronze 12 
with the original standards (omitting Shuckburgh’s scale). The results are tH^ follow- 
ing;— (P=0-003576). 
By 100 obsenations at 56°-04 Fahr., Bronze 12 = Ordnance lA— 0'^-0582 
=:36‘"-000219 
By 100 observations at 56°-5 Fahr., Bronze 12 = Ordnance 2A — 0''T275 
= 36-000093 
Also, j. 
By 75 observations. Low Moor A = Ordnance lA+0-06G3 = 35-999962 
By 55 obseiwations. Low Moor A = Ordnance 2A+0-0102 = 35-999930 
Mean .... =35-999946 
and 
By 200 obs. (reduced separately) at 62° Fahr., Bronze 12 = Low Moor A-f -000149 
= 36-000095 
In a similar way, through a bar of Swedish iron. 
Bronze 12 = 36-000063 
By 160 observations at 57°-58 Fahr., Bronze 12=R. Soc.4-0''-1727 = 35-999982. 
From these, Mr. Sheepshanks concluded 
Bronze 12 = 36-000043 
at the fundamental temperature 62° Fahrenheit. 
(Different reductions gave 36-000034 and 36-000048.) 
In the winter of 1849-1850 Mr. Sheepshanks made a series of experiments for the 
thermometric expansions of Bronze, Brass, and Low Moor Iron. The different tem- 
peratures were given to the bars by pouring in water at different temperatures into the 
external box : this, I believe, is the first occasion on which it was so used. The quan- 
