LIEUT. -COL. A. E. CLARKE ON STANDARDS OF LENGTH. 
465 
This differs but 2-36 from our former result. The mean of the two is 
M.=1-09369651Y m , 
the probable error of which we may well assume to be about +2-00. 
The length of the American metre No. 6, according to the Report, Appendix No. 26, 
is, at 32°, less than the “ Committee metre ” by 3-41 fifteen thousandths of an inch, that is 
6-31. 
By more recent comparisons made in March 1869 (kindly communicated by J. E. 
Hilgakd, Esq.), No. 6 is short by 3 - 2 ten thousandths of an inch, that is 
8-89. 
Taking the mean of these, we infer the length of the American standard metre to be 
T09360411Y 5S . 
The Report referred to mentions that “ besides the Committee metre there is in the 
collection of the Coast Survey another iron metre of special value, having been made by 
Lenoir, the artist who performed the mechanical operations in the preparation of the 
original metres. It is designated as the “ Lenoir metre,” and has been found, by 
accurate comparisons with the Committee metre, to be shorter than the latter by 
0 m -0000258.” This quantity is 28-21 millionths of a yard. Hence the Lenoir metre 
has for length, 
Lenoir metre=L09357590Y M . 
The Russian Rouble Toises. 
The Russian Double Toise P, of which observations are now to be recorded, is the 
same bar that was compared at Southampton in 1865. In those comparisons the woollen 
packing which surrounded the bar was allowed to remain undisturbed. It appears, 
however, from a subsequent communication from M. Struve, that the bar has been 
accustomed to be compared with the packing removed, and only a thin covering of cloth 
remaining wrapped round it. It was therefore judged expedient byM. Struve that the 
bar should be returned to Southampton for further comparisons to be made without the 
woollen packing. Moreover, in the comparisons of this bar made in Russia, the contacts 
are said to have been made at the centres of the disks, and not at the points corre- 
sponding to the maximum of length, at which the contacts were made here. 
The small terminal cylinder of this bar has a diameter of 0-25 inch, and the centre 
of curvature of the terminal surface, instead of being, as it should be, in the axis of the 
cylinder, is 0-025 inch above it. Let A B be the horizontal axis of the cylinder, a b that 
of the cylinder of another bar brought up to contact. Suppose that the centre of the 
