The micrometer is at zero when the two edges are brought exactly together.
The micrometer shown in fig.
The micrometer is clamped in FIG.
micrometer with the upper side of the box removed.
A still further facility was given to the use of the filar micrometer by the introduction of clockwork, which caused the telescope automatically to follow the diurnal motion of a star, and left the observer's hands entirely at liberty.'