THE KEW Js^ATIOXAL STANDAED OE LENGTH, AND ITS PEINCIPAL COPIES. 601 
purpose. To facilitate the comparison with the Ordnance Standards, two bars of 
wrought iron (Low Moor and Swedish) were prepared, similar in form to the bronze 
and brass bars, and were used as intermediaries ; some comparisons were however made 
directly with the Ordnance Bars. Then it Avas necessary to express the length of 
Shuckbuegh’s Scale and of the Royal Society’s and Ordnance Standards in terms of the 
Lost Imperial Standard. For Shuckbuegh’s and the Royal Society’s Scale, Mr. Siieep- 
SHAXES adopted Katee’s and Baily’s values. For the Ordnance Bars, a very troublesome 
investigation Avas undertaken. On account of the difference of metal, it Avas necessary 
to examine the graduation of the thermometers; and the result Avas, that Muephy’s 
thermometer L requmed the correction — 1°T2, Muephy’s R — 0°-95, lA -l-0°‘7, and 
2A — 0°’4. Baily’s thermometer appeared nearly correct. Then there Avas a discus- 
sion, at great length, of the personal equations of the different observers, in the observa- 
tion of the different dots of the Imperial Standard, and of the Ordnance Standards. 
Long study wmuld be necessary to enable any person to exhibit all the steps of these 
operations in a clear and logical form. The Aulues which Mr. Sheepshanks appears to 
haA'e adopted for the lengths of the tAvo Ordnance Bars in terms of the Imperial Stand- 
ard, at the temperature 62° Faheenheit, are IA= 35-999716 mches, 2A— 35-999892 
inches. Finally, from these various sources, Mr. Sheepshanks inferred the value of 
Brass 2, and communicated it to the Members of the Committee in the folloAving paper. 
“ Statement of the means employed for obtaining an Authentic Copty of the Lost Imperial 
Standard Yard. By the Bev. R. Sheepshanks. 
“ As I haA’e noAv completed the first set of observations for restoring the lost Standard, 
I AA’ish to present the results to the Committee. 
“ I haA’e taken a brass bar (marked No. 2) as my term of comparison. This is held by 
its middle, and floats as nearly as possible in mercury. The comparisons haA'e been 
made carefully AAuth the heA primary evidence of the lost Imperial Standard. 
“ I am A’eiy’ much surprised, and not a little mortified, that this evidence should be so 
scanty ; still I trust that it is sufficient for my purpose, Avhich is simply to procure a 
copy of the Imperial Standard, Avhich is at least as accurate as any results derived from, 
or referred to it. A short notice of our measures of length Avill not be out of place. 
All the accurate scales Avhich have been made Avithin the last hundred years can be 
traced back, errors excepted, to the yard laid off by Geaham, on a bar made for the 
Royal Society in 1742. I shall call this Geaham’s bar, to distinguish it from other- 
scales belonging to the same Society. Upon this bar, Geaham laid doAvn a yard taken 
from a Standard kept at the ToAver (this yard is marked E on Geaham’s bar, and is 
called by me Geaham’s Toiver Yard E)^ but not with any particular care*; and Avhen 
* It is stated in the Philosophical Transactions, 1742-3, p. 185, that “ Mr. Geaham did with the greatest 
care lay off the length of three English feet from the Standard of a Yard kept in the Tower of London.” As 
the Tower Standard was a flat scale, this conld he done with great accuracy. "WTien both were compared 
MDCCCLVII. 4 E 
