THE ACCURATE MEASUREMENT OF TIME. 66g 



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 as- 

 certained, 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, \\\\\ 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 mo- 

 tion. 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 an- 

 other'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 



