length of the pendulum vibrating seconds. 57 
carefully measured with the micrometer, and from a mean of 
eight observations, the greatest difference between which did 
not exceed one division, was found to be 329,09 divisions. 
The same was done with the pieces B and b, and the dis- 
tance of the lines from a mean of sixteen observations ap- 
peared to be 366,96 divisions. 
The knife edges being adjusted as nearly as possible 
parallel to each other, the pieces A, a, and B, b, were placed 
in contact with those parts of the knife edges on either side 
of the bar, on which the vibrations were to be performed, and 
were retained in their places by the pressure of slight springs, 
attached to the mahogany case. 
The microscopes were now brought over the pieces A and 
a, so as for the lines before described to bisect the cross 
threads, when the division of the micrometer was noted. 
The same was done with the pieces B and b ; and the divi- 
sion of the micrometer was also registered. 
The pendulum being removed, the standard scale* was 
placed beneath the micrometer, and its zero being made to 
bisect the angles of the fixed microscope, the cross threads of 
the micrometer microscope were brought to 39,4 of the scale, 
and the revolutions and parts of the micrometer were noted. 
From these data, and the respective distances of the lines 
on A and a, and on B and b, when the pieces were in con- 
tact, the distance of the knife edges on either side of the bar 
may be readily obtained, and the mean being taken, will ob- 
viously correct any error arising from a want of perfect 
parallelism in the knife edges. 
It is very generally believed that measurements from a 
* The scale constantly referred to, is Sir George Shuckburgh’s standard. 
MDCCCXVIII. I 
