io 4 Capt . Kater tm length of the French metre 
compared with a standard metre by M. Arago, with all that 
care and ability which he is so well known to possess, and 
which so delicate an operation requires. The result was, that 
the distance between the lines was found to be less than a 
metre by tooo °f a millimetre or ,00069 of an inch. 
The same micrometer microscopes were used in the com- 
parisons which I am about to detail, as have been already 
described in my account of experiments on the length of the 
pendulum, in the Philosophical Transactions of the present 
year, and as the length of the metre is nearly 39,4, inches, 
I was enabled to refer it to the same divisions of Sir George 
Shuckburgh’s scale as I had employed in the measurement of 
the pendulum. 
I commenced with the metre a traits. It was placed in 
contact with the standard scale, their surfaces being in the 
same plane. An excellent thermometer was laid upon the 
scale, and a piece of thick leather was placed upon its bulb 
in order to prevent its being affected by heat from the person 
of the observer. 
The whole was suffered to remain in this state for two or 
three days, after which the following observations were 
made at various times, the microscopes being brought alter- 
natety over the metre and the scale. The value of each 
division of the micrometer is zjiTJ °f an 
* For the manner in which this value was obtained, see page 51 of the preceding, 
paper. 
