length of the pendulum vibrating seconds . 
53 
Divisions of the micrometer. 
502.0 
501,5 
501.0 
5°2,o 
501.5 
502.0 
502,0 
502.5 
502,0 
502.0 
502.5 
501.0 
501.5 
502.0 
501.0 
502.5 
501.0 
500.0 
500,0 
500.5 
Mean 501,5 
The mean is 501,5, and the greatest difference from the mean 
only one division, amounting to T of an inch, a degree 
of accuracy truly surprising, when it is considered that all 
errors of observation are included in this minute quantity. 
Comparison of the different standards. 
The microscopes being placed at the distance of 39,4 in- 
ches, were advanced by single tenths, from zero of the scale 
through the space of two inches, and the mean of twenty 
measurements thus obtained being compared with the dis- 
tance from zero to 39,4 inches, this last was found to be 
