Popular Science Monthly 



723 



The framework removed to reveal the train, escapement and hairspring of a watch 



The hairspring Is never-ceasing in its vigilance. If you move suddenly you may shorten the swing of the 

 balance; but the hairspring instantly checkmates this by reducing the speed in exact proportion to the 

 reduction in the extent of motion. Again, the balance may have its journey lengthened above the average 

 by an increase of power, or by an external motion (as when you happen to give the watch a "twisting" 

 motion). In this case, the hairspring instantly increases the speed of the balance in direct proportion to 

 the increase of the extent in motion. Now, you understand how the hairspring helps to make good time- 

 keeping possible, by making the balance "space off" portions of time which are equal under all conditions. 

 In cheap watches the hairspring is not "adjusted to isochronism." In better grades the isochronal (uniform 

 timing) adjustment is secured by forming the hairspring's outer coil into a certain shape, found for each 

 watch individually by experiment and trial. The practical application of isochronal adjustment requires 

 high intelligence and skill on the part of the watchmaker. Yet no watch keeps jjerfect time constantly 



with the changes in the hairspring at 

 different temperatures. Cheap watches 

 are not adjusted to temperatures. 



Fine watches are put through a series of 

 adjustments to positions, in addition to 

 those for isochronism and temperatures. 

 In position-adjusting, the mechanism of the 

 watch is altered where necessary so that the 

 frictions affecting the moving parts, hence 

 the timekeeping, are alike whether the 

 watch is run lying down or hanging, or in 

 any other position. 



Why Has a Good Watch Jewels? 



What are the advantages of jewels in a 

 watch? In the early days of watchmaking, 

 the bearings for the pivots of the moving 



parts were simply holes drilled in the metal 

 of the framework. This is still the case in 

 cheap watches. But good modern watches 

 have the bearings made by drilling holes in 

 hard ruby or sapphire disks. These disks 

 are mounted in the framework, and in their 

 highly polished holes the pivots turn with 

 much less friction than in metal bearings. 

 A first-class watch can be expected to 

 keep time to within a half minute a week, 

 while in use by an active person. Worn by 

 a sedate, careful person, a good watch may 

 run even better. It then remains for the 

 owner to have the good timekeeping quality 

 of his watch maintained by having it 

 cleaned and oiled by a reliable watchmaker, 

 at least every two years. 



