was ±.000015; hence the total error due to D would be at most .00004. The
tape has been sent to Professor Rogers, of Cambridge, for comparison, to
confirm the result.



The Speed of Rotation.


This quantity depends on three conditions. It is affected, first, by an
error in the rate of the standard; second, by an error in the count of the
sound beats between the forks; and third, by a false estimate of the
moment when the image of the revolving mirror is at rest, at which moment
the deflection is measured.

The calculated probable error of the rate is .000016. If this rate should
be questioned, the fork can be again rated and a simple correction
applied. The fork is carefully kept at the Stevens Institute, Hoboken, and
comparisons were made with two other forks, in case it was lost or
injured.

In counting the sound beats, experiments were tried to find if the
vibrations of the standard were affected by the other fork, but no such
effect could be detected. In each case the number of beats was counted
correctly to .02, or less than .0001 part, and in the great number of
comparisons made this source of error could be neglected.

The error due to an incorrect estimate of the exact time when the images
of the revolving mirror came to rest was eliminated by making the
measurement sometimes when the speed was slowly increasing, and sometimes