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Sept. 4, 1873] 
NATURE 
367 
ON THE SCIENCE OF WEIGHING AND 
MEASURING, AND THE STANDARDS OF 
WEIGHT AND MEASURE * 
IV. 
THE IMPERIAL STANDARD YARD 
Sao immediate superintendence of the construction 
of the new standard yard was entrusted, in the 
first instance, to Mr. Baily, who conducted all the pre- 
liminary investigations and experiments. After his death 
in August 1844, it was undertaken by Mr. Sheepshanks, 
by whom and under whose direction by far the largest 
proportion of the actual operations was carried out, and 
all the comparing operations of the several standards of 
length made, up to the period of his death in August 
1855. By this time the work was so far completed that 
not a single additional comparison of line measures was 
required. The detailed account of the construction of 
the new standard yard, and its verified copies, was then 
undertaken by the Astronomer Royal, with the aid of the 
documents left by Mr. Baily and Mr. Sheepshanks ; and 
the winding-up of the*work of the Commission, and the 
Each of these standard yards consisted of a solid brass 
bar 1°05 inch square in section, and 39°73 inches long. 
Near each end of the upper surface gold pins or studs 
ol inch in diameter were inserted, and points or dots 
were marked upon the gold to determine the length of 
the yard. The comparing apparatus in use at that 
period consisted of a beam compass with two fine 
measuring points, which could be adjusted to the dots on 
the standard measures under comparison. But the re- 
sult of numerous comparisons of this kind made from 
time to time previously to the destruction of the standard 
in 1834, had been to leave the edges of the holes in- 
dented and irregularly worn away, so that the original 
centre was very difficult to ascertain. Mr. Baily, who 
had made some comparisons with this standard yard 
in the early part of the year 1834, describes the holes as 
appearing, under a microscope, like the miniature crater 
of a volcano. 
The length of the standard yard of 1758, had been 
based upon that of the then existing Exchequer standard 
yard, which had been constructed in the reign of Queen 
Elizabeth in 1588, and upon the length of the Koyal 
Society’s standard yard, constructed as a scientific 
standard measure in 1742. It had been determined, upon 
* Continued from p. 329. 
distribution of the scientifically verified copies of the 
standards also devolved upon the Astronomer Royal, as 
the chairman. The magnitude of the operations may be 
estimated from the fact of the number of micrometer 
readings for all the comparisons exceeding two hundred 
thousand; and amongst the operations it was found 
necessary to construct an entirely new system of ther- 
mometers. It should not be forgotten that the scientific 
gentlemen who bestowed so much of their valuable time, 
attention, and labour, during several years upon the 
experiments and observations for the important object of 
the restoration of the national standard of length, de- 
clined to accept any pecuniary remuneration. 
_ The length of the new standard yard was determined 
in a similar manner to the determination of the weight of 
the new standard pound, by taking the mean length of 
the most authoritative standards which constituted the 
best primary evidence of the lost standard yard. 
This standard measure of length had been constructed 
by Bird, in 1760, under the directions of the Committee 
of the House of Commons on Weights and Measures, 
first appointed in 1758. Its length was taken from a 
similar yard which had been constructed by Bird in 1758. 
Fic. 8.—Standard Winchester Pushel of Henry VII } size. 
comparison, to agree as nearly as possible with these two 
authoritative measures of a yard. 
The two standard bars of 1758 and 1760 were found 
amongst the ruins of the Houses of Parliament, but they 
were too much injured to indicate the measure of a yard 
which had been marked upon them, 
Bird’s standard yard of 1760 had been left in the 
custody of the clerk of the House of Commons, and no 
legal authority was given to it as a standard of length 
until the passing of the Act 5 Geo. IV. C. 74, in 1824, 
already referred to. Meanwhile, other scientific standards 
of length had been constructed which may now be noticed. 
In 1785, the first geodesical operations were begun, 
upon which the Ordnance Survey of the United Kingdom 
has since been founded, by General Roy’s measurement 
of the base on Hounslow Heath. The standard used in 
the first instance for that purpose was that known as 
General Roy’s scale, 42 inches in length, and constructed 
by Mr. Bird. This scale was based, not on the legal 
Exchequer Standard, but upon the Royal Society’s scale, 
with which the whole length of the first 36 inches of 
General Roy’s scale was compared, this constituting the 
Ordnance yard. Two standard yards of superior con- 
struction, belonging to the Ordnance Department, 
were placed at the disposal of the Standards Commission. 
