Page:Popular Science Monthly Volume 26.djvu/687

Rh by shaping the pivots, blunting them or sharpening, according as it is found to be necessary.

The third difficulty named was that of preventing the different pressures of the mainspring (as when it is tightly wound or nearly run down) from altering the rate of the watch. This is effected in the following manner: It is found to be a fact that there is a point in any hair-spring at which, if it be secured, it will carry the balance-wheel at the same rate no matter what the force of the train. This point can only be discovered by experiment, and the discovery of it constitutes the adjustment of the watch to what is called "isochronism." By continually shifting the point where the hair-spring is pinned, a point is finally discovered where the watch goes at a uniform rate, which may be too fast or too slow, but it is uniform. This point ascertained, the watch is then made to keep diurnal time by shifting the screws in the circumference of the balance.

Of course, it greatly increases the expense of a watch to add these fine touches by the best skilled workmen; and yet so perfect is the machinery to-day and so closely does the watch when first put together conform to the well-understood proportions that in point of fact a large per cent of them are found to be correct, and need little or no adjusting. In this case they are simply marked "Adjusted," and sent to market. The leading American factories have discontinued the manufacture of watches which have not compensating balances, so that, even though the watch be of cheaper grade, it will still run far better through all weathers than the best watches with a solid balance.

In the American watch we may well take a patriotic pride, for it is the best watch in the world; and, what is more, it is being imitated everywhere. Its only real rival is the Swiss watch, the better grades of which can hardly be said to be inferior as time-keepers to American watches. The cheaper grades, however, will not rank with the same grades of our watches.

After a watch has been given all the advantages of adjustment described, it is interesting to inquire how closely it will run. But, lest we expect too much, it is important that we keep in mind that a watch is at great disadvantage in comparison with any other time-keeper, for it can depend upon no uniformity either of rest or of motion. No two men's habits of life are such as to give their watches exactly the same jar and disturbance. One man's watch is laid down at night, and another's is hung up; one man's is in the cold, and another's is where it is warm; one man is much upon the rail, and another seldom travels at all; one man's habits of life take him into those sorts of dust which soon clog the oil of his watch, another is never in any dust. Add to all these considerations one more, namely, that a watch will run a little freer, and hence a little faster, when the oil is fresh, and of course will slow down as the oil gets old, and we