_A^2_ will be free.

We would beg to say here there is no escape wheel made which requires
the same extreme accuracy as the chronometer, as the tooth spaces and
the equal radial extent of each tooth should be only limited by our
powers toward perfection. It is usual to give the detent a locking of
about two degrees; that is, it requires about two degrees to open it,
counting the center of fluxion of the detent spring _E_ and five degrees
of balance arc.

FITTING UP OF THE FOOT.

Several attempts have been made by chronometer makers to have the foot
_F_ adjustable; that is, so it could be moved back and forth with a
screw, but we have never known of anything satisfactory being
accomplished in this direction. About the best way of fitting up the
foot _F_ seems to be to provide it with two soft iron steady pins (shown
at _j_) with corresponding holes in the chariot, said holes being
conically enlarged so they (the pins) can be bent and manipulated so the
detent not only stands in the proper position as regards the escape
wheel, but also to give the detent spring _E_ the proper elastic force
to return in time to afford a secure locking to the arresting tooth of
the escape wheel after an impulse has been given.

If these pins _j_ are bent properly by the adjuster, whoever afterwards
cleans the chronometer needs only to gently push the foot _F_ forward so
as to cause the pins _j_ to take the correct positions as determined by
the adjuster and set the screw _l_ up to hold the foot _F_ when all the
other relations are as they should be, except such as we can control by
the screw _G_, which prevents the locking jewel from entering too deeply
into the escape wheel.

In addition to being a complete master of the technical part of his
business, it is also desirable that the up-to-date workman should be
familiar with the subject from a historical point of view. To aid in
such an understanding of the matter we have translated from "L'Almanach
de l'Horologerie et de la Bijouterie" the matter contained in the
following chapter.

CHAPTER IV.

HISTORY OF ESCAPEMENTS.

It could not have been long after man first became cognizant of his
reasoning faculties that he began to take more or less notice of the
flight of time. The motion of the sun by day and of the moon and stars
by night served to warn him of the recurring periods of light and
darkness. By noting the position of these stellar bodies during his
lonely vigils