Let us further suppose the diameter of our actual escape wheel to be .26”, and we were constructing a watch after the lines of our drawing.  By “lines,” in this case, we mean in the same general form and ratio of parts; as, for illustration, if the distance from the intersection of the arc a with the line b to the point B was one-fifteenth of the diameter of the escape wheel, this ratio would hold good in the actual watch, that is, it would be the one-fifteenth part of .26”.  Again, suppose the diameter of the escape wheel in the large drawing is 10” and the distance between the centers A B is 5.78”; to obtain the actual distance for the watch with the escape wheel .26” diameter, we make a statement in proportion, thus:  10 :  5.78 ::  .26 to the actual distance between the pivot holes of the watch.  By computation we find the distance to be .15”.  These proportions will hold good in every part of actual construction.

All parts—­thickness of the pallet stones, length of pallet arms, etc.—­bear the same ratio of proportion.  We measure the thickness of the entrance pallet stone on the large drawing and find it to be .47”; we make a similar statement to the one above, thus:  10 :  .47 ::  .26 to the actual thickness of the real pallet stone.  By computation we find it to be .0122”.  All angular relations are alike, whether in the large drawing or the small pallets to match the actual escape wheel .26” in diameter.  Thus, in the pallet D, Fig. 93, the impulse face, as reckoned from B as a center, would occupy four degrees.

MAKE A LARGE ESCAPEMENT MODEL.

Reason would suggest the idea of having the theoretical keep pace and touch with the practical.  It has been a grave fault with many writers on horological matters that they did not make and measure the abstractions which they delineated on paper.  We do not mean by this to endorse the cavil we so often hear—­“Oh, that is all right in theory, but it will not work in practice.”  If theory is right, practice must conform to it.  The trouble with many theories is, they do not contain all the elements or factors of the problem.

[Illustration:  Fig. 94]

Near the beginning of this treatise we advised our readers to make a large model, and described in detail the complete parts for such a model.  What we propose now is to make adjustable the pallets and fork to such a model, in order that we can set them both right and wrong, and thus practically demonstrate a perfect action and also the various faults to which the lever escapement is subject.  The pallet arms are shaped as shown at A, Fig. 94.  The pallets B B’ can be made of steel or stone, and for all practical purposes those made of steel answer quite as well, and have the advantage of being cheaper.  A plate of sheet brass should be obtained, shaped as shown at C, Fig. 95.  This plate is of thin brass, about No. 18, and on it are outlined the pallet arms shown at Fig. 94.