It will be seen the impulse roller is staked flat against the hub E of the balance staff.  The unlocking roller, or, as it is also called, the discharging roller, C, is usually thinner than the impulse roller and has a jewel similar to the impulse jewel a shown at f.  This roller is fitted by friction to the lower part of the balance staff and for additional security has a pipe or short socket e which embraces the balance staff at g.  The pipe e is usually flattened on opposite sides to admit of employing a special wrench for turning the discharging roller in adjusting the jewel for opening the escapement at the proper instant to permit the escape wheel to act on the impulse jewel a.  The parts which go to make up the detent D consist of the “detent foot” F, the detent spring h, the detent blade i, the jewel pipe j, the locking jewel (or stone) s, the “horn” of the detent k, the “gold spring” (also called the auxiliary and lifting spring) m.  This lifting or gold spring m should be made as light and thin as possible and stand careful handling.

We cannot impress on our readers too much the importance of making a chronometer detent light.  Very few detents, even from the hands of our best makers, are as light as they might be.  We should in such construction have very little care for clumsy workmen who may have to repair such mechanism.  This feature should not enter into consideration.

We should only be influenced by the feeling that we are working for best results, and it is acting under this influence that we devote so much time to establishing a correct idea of the underlying principles involved in a marine chronometer, instead of proceeding directly to the drawing of such an escapement and give empirical rules for the length of this or the diameter of that.  As, for instance, in finishing the detent spring h, suppose we read in text books the spring should be reduced in thickness, so that a weight of one pennyweight suspended from the pipe j will deflect the detent 1/4”.  This is a rule well enough for people employed in a chronometer factory, but for the horological student such fixed rules (even if remembered) would be of small use.  What the student requires is sound knowledge of the “whys,” in order that he may be able to thoroughly master this escapement.

FUNCTIONS OF THE DETENT.

We can see, after a brief analysis of the principles involved, that the functions required of the detent D are to lock the escape wheel A and hold it while the balance performs its excursion, and that the detent or recovering spring h must have sufficient strength and power to perform two functions:  (1) Return the locking stone s back to the proper position to arrest and hold the escape wheel; (2) the spring h must also be