+.70. Cap of pier to revolving mirror.
+.33. Correction for stretch of tape.
+.12. Correction for length of tape.
--------
1986.23. True distance between mirrors.



Rate of Standard Ut₃ Fork.


The rate of the standard Ut₃ fork was found at the Naval Academy, but as
so much depended on its accuracy, another series of determinations of its
rate was made, together with Professor Mayer, at the Hoboken Institute of
Technology.


_Set of determinations made at Naval Academy._

The fork was armed with a tip of copper foil, which was lost during the
experiments and replaced by one of platinum having the same weight,
4.6 mgr. The fork, on its resonator, was placed horizontally, the platinum
tip just touching the lampblacked cylinder of a Schultze chronoscope. The
time was given either by a sidereal break-circuit chronometer or by the
break-circuit pendulum of a mean-time clock. In the former case the
break-circuit worked a relay which interrupted the current from three
Grove cells. The spark from the secondary coil of an inductorium was
delivered from a wire near the tip of the fork. Frequently two sparks near
together were given, in which case the first alone was used. The rate of