[Illustration:  Fig. 105]

[Illustration:  Fig. 106]

A good way to get up the parts shown in Fig. 106 is to take a disk of thick sheet brass about 1” in diameter and insert in it a piece of brass wire about 1/4” diameter and 3/8” long, through which drill axially a hole to receive the wire k.  After the jaws B’’ are clamped on the pallet staff, we set the index arc C so the hand B’ will indicate the angular motion of the pallet staff.  By placing the index hand B on the balance staff we can get at the exact angular duration of the engagement of the jewel pin in the fork.

Of course, it is understood that this instrument will also measure the angles of impulse and lock.  Thus, suppose the entire angular motion of the lever from bank to bank is ten degrees; to determine how much of this is lock and how much impulse, we set the index arc C so that the hand B’ marks ten degrees for the entire motion of the fork, and when the escapement is locked we move the fork from its bank and notice by the arc C how many degrees the hand indicated before it passed of its own accord to the opposite bank.  If we have more than one and a half degrees of lock we have too much and should seek to remedy it.  How?  It is just the answers to such questions we propose to give by the aid of our big model.

DETERMINATION OF “RIGHT” METHODS.

“Be sure you are right, then go ahead,” was the advice of the celebrated Davie Crockett.  The only trouble in applying this motto to watchmaking is to know when you are right.  We have also often heard the remark that there was only one right way, but any number of wrong ways.  Now we are inclined to think that most of the people who hold to but one right way are chiefly those who believe all ways but their own ways are wrong.  Iron-bound rules are seldom sound even in ethics, and are utterly impracticable in mechanics.

We have seen many workmen who had learned to draw a lever escapement of a given type, and lived firm in the belief that all lever escapements were wrong which were not made so as to conform to this certain method.  One workman believes in equidistant lockings, another in circular pallets; each strong in the idea that their particular and peculiar method of designing a lever escapement was the only one to be tolerated.  The writer is free to confess that he has seen lever escapements of both types, that is, circular pallets and equidistant lockings, which gave excellent results.

Another mooted point in the lever escapement is, to decide between the merits of the ratchet and the club-tooth escape wheel.  English makers, as a rule, hold to the ratchet tooth, while Continental and American manufacturers favor the club tooth.  The chief arguments in favor of the ratchet tooth are:  (a) It will run without oiling the pallets; (b) in case the escape wheel is lost or broken it is more readily replaced, as all ratchet-tooth escape wheels are alike, either for circular pallets or equidistant lockings.  The objections urged against it are:  (a) Excessive drop; (b) the escape wheel, being frail, is liable to be injured by incompetent persons handling it; (c) this escapement in many instances does require to have the pallets oiled.