It will not do, however, to accept, and take it for granted that the escape-wheel teeth are all right, because in many instances they have been stoned away and made too short; but if we accept this condition as being the case, that is, that the escape-wheel teeth are too short, what is the workman going to do about it?  The owner of the watch will not pay for a new escape wheel as well as a new cylinder.  The situation can be summed up about in this way, that we will have to make the best we can out of a bad job, and pick out and fit a cylinder on a compromise idea.

In regard to picking out a new cylinder, it may not do to select one of the same size as the old one, from the fact that the old one may not have been of the proper size for the escape wheel, because, even in new, cheap watches, the workmen who “run in” the escapement knew very well the cylinder and escape wheel were not adapted for each other, but they were the best he had.  Chapter II, on the cylinder escapement, will enable our readers to master the subject and hence be better able to judge of allowances to be made in order to permit imperfect material to be used.

In illustration, let us imagine that we have to put in a new cylinder, and we have none of precisely the proper size, but we have them both a mere trifle too large and too small, and the question is which to use.  Our advice is to use the smaller one if it does not require the escape-wheel teeth to be “dressed,” that is, made smaller.  Why we make this choice is based on the fact that the smaller cylinder shell gives less friction, and the loss from “drop”—­that is, side play between the escape-wheel teeth and the cylinder—­will be the same in both instances except to change the lost motion from inside to outside drop.

In devising a system to be applied to selecting a new cylinder, we meet the same troubles encountered throughout all watchmakers’ repair work, and chief among these are good and convenient measuring tools.  But even with perfect measuring tools we would have to exercise good judgment, as just explained.  In Chapter II we gave a rule for determining the outside diameter of a cylinder from the diameter of the escape wheel; but such rules and tables will, in nine instances out of ten, have to be modified by attendant circumstances—­as, for instance, the thickness of the shell of the cylinder, which should be one-tenth of the outer diameter of the shell, but the shell is usually thicker.  A tolerably safe practical rule and one also depending very much on the workman’s good judgment is, when the escape-wheel teeth have been shortened, to select a cylinder giving ample clearance inside the shell to the tooth, but by no means large enough to fill the space between the teeth.  After studying carefully the instructions just given we think the workman will have no difficulty in selecting a cylinder of the right diameter.

MEASURING THE HEIGHTS.