THE NEW NATIONAL STAND AED OF LENGTH, AND ITS PEINCIPAL COPIES. 629 
pendulum as observed in atmospheric air to the vibrations in vacuum, ought to be 
greatly increased. Sabine immediately repeated these experiments, with special refer- 
ence to the form of pendulums which had been usually employed in England ; and after 
him, Baily extended the experiments to pendulums of various forms*. The residt for 
British pendulums is, that Kater’s correction ought to have been multiplied by 1'655 
nearly. The corresponding error in the length of the yard-standard is a quantity very 
conspicuous to the naked eye. 
There is also great doubt on the propriety of the reduction to the level of the sea. 
It may not be out of place to anticipate here an investigation begun by myself in 
1843 and completed in 1844 or 1845 (sufficiently early to be used in the observations 
hereafter to be mentioned), and printed in the Royal Astronomical Society’s Memoirs, 
vol. XV. It relates to the value of the intervals (supposed equal) which ought to exist 
between different supports of a bar, each support exerting the same vertical pressure 
upwards, in order that the interval between two points upon the surface of the bar may 
not be altered by the flexure. The resulting interval of supports = 
length of bar 
where 
n is the number of supports. It is easily seen that the arrangement of levers by which 
equal pressures upwards may be exerted at four or eight points, is very simple. 
I beheve that the matters which I have cited will give a correct idea of the advances 
made in the science of standards since the Act of 1824. It had been shown that it was 
imprudent in any case to trust to points or lines traced on the surface of a bar, and 
therefore for delicate purposes, supposing the standard to be a line-measure, only Bvo 
lines or points ought to be used, sunk to the middle of the bar’s thickness. It had been 
shown that it was imprudent to lay the bar upon a table or upon fixed supports of any 
kind, and therefore the bar must be stiff enough to bear to be supported upon a few 
points at which rollers could be conveniently applied. It had been shown that the 
physical reference provided in the Act of Parliament of 1824 was erroneous in one par- 
ticular and doubtful in another; and, as it seemed likely that similar uncertainties 
might be found in any other physical reference, the conviction was gradually rising that 
it would be better to trust, for restoration, to attested copies of the Standard. The 
question of the propriety of adopting line-measure or end-measure for the National 
Standard, which in this countiy had been practically decided (without a single opposing 
instance as regarded accurate standards) in favour of line-measure, had again been raised 
by Bessel’s adoption of end-measure. 
On 1834, October 16, occurred the fire at the Houses of Parliament, in which the 
Standards were destroyed. The bar of 1760 was recovered, but one of its gold pins 
bearing a point was melted out, and the bar was otherwise injured. 
On 1838, May 11, the Right Honourable T. Spring Rice (now Lord Monteagle), 
Chancellor of the Exchequer, requested a Committee to consider and report upon the 
course which under all circumstances it would be best to follow. 
MDCCCLVII, 
* See the Philosophical IVansactions, 1829 and 1832. 
4 N 
