course has a tendency to avoid cockling or buckling of the detent spring
_E_. Such adjusters also set the impulse jewel slightly oblique, so as
to lean on the opposite angle of the tooth. Our advice is to set both
stones in places corresponding to the axis of the balance staff, and the
escape-wheel mobiles.

THE DETENT SPRING.

[Illustration: Fig. 144]

It will be noticed we have made the detent spring _E_ pretty wide and
extended it well above the blade of the detent. By shaping the detent in
this way nearly all the tendency of the spring _E_ to cockle is
annulled. We would beg to add to what we said in regard to setting
jewels obliquely. We are unable to understand the advantage of
wide-faced stones and deep teeth when we do not take advantage of the
wide surfaces which we assert are important. We guarantee that with a
detent and spring made as we show, there will be no tendency to cockle,
or if there is, it will be too feeble to even display itself. Those who
have had extended experience with chronometers cannot fail to have
noticed a gummy secretion which accumulates on the impulse and
discharging stones of a chronometer, although no oil is ever applied to
them. We imagine this coating is derived from the oil applied to the
pivots, which certainly evaporates, passes into vapor, or the remaining
oil could not become gummy. We would advise, when setting jewels (we
mean the locking, impulse and discharging jewels), to employ no more
shellac than is absolutely necessary, depending chiefly on metallic
contact for security.

DETAILS OF CONSTRUCTION.

We will now say a few words about the number of beats to the hour for a
box or marine chronometer to make to give the best results. Experience
shows that slow but most perfect construction has settled that 14,400,
or four vibrations of the balance to a second, as the proper number, the
weight of balance, including balance proper and movable weights, to be
about 51/2 pennyweights, and the compensating curb about 1-2/10" in
diameter. The escape wheel, 55/100" in diameter and recessed so as to be
as light as possible, should have sufficient strength to perform its
functions properly. The thickness or, more properly, the face extent of
the tooth, measured in the direction of the axis of the escape wheel,
should be about 1/20". The recessing should extend half way up the
radial back of the tooth at _t_. The curvature of the back of the teeth
is produced with the same r