STEEL BRAss expansion of the brass portion causing the bar to curve upward. If cold was applied instead of heat the bar would be deflected in the op posite direction (as shown in Figure 4). Figure 5 shows a watch balance, in which the arms and the inner portion of the rim are of steel, the outer portion of the rim being of brass fused to the steel rim, the rim being severed at two points, near the arms, thus allowing freedom for the movement of the rim under the changes of temperature. Figure 6 shows this balance when under the influence of heat. Figure 7 shows a complete balance, having a number of screws with relatively heavy heads located at varying distances around the rim of the balance. Figure 8 shows the finished balance under influence of heat. The effect of heat is to curve the rim inward, thus reducing the size of the balance—the endeavor, of course, being to maintain the effective dia meter unchanged. But the quantities involved are so extremely minute that additional and more delicate adjlistments meat be peoeided. It will be observed that on Figure 8 the loca tions of the balance rim screws are numbered from I to 12 on each half of the balance. Also note that screws numbered 1 and 6 have shorter heads and longer bodies than the others. Also note that while these four screws are screwed in only part wan the others are screwed down to the head. These four screws are desig nated as °meantime screws,' since by screwing them in further the active diameter of the balance is reduced, that is, while the actual weight of the balance remains unchanged, a very minute portion of the weight is carried nearer to the centre of the balance, with the result of very slightly increasing the rapidity of its vibration. A watch balance vibrating precisely 18,000 times each hour will keep per fect time. But if it should vibrate 18,001 times an hour the watch would gas two and toolsidits minds: is • month. &Opole that owing to a change in temperature the self compensation of the balance, as before de scribed, should be iusuificient, and the watch should lose because qf the increase in heat it would show that it was 'under compen sated.' In such case it might suffice to simply change the location of some of the rim screws, for instance, to move screws number 4 to locations ;Lumber 11. Such a change of
location would not at all affect the actual weight of the balance, but would modify the vibrational weight, because when the screws were in location 11 they would be near the free end of the rim, and the distortion of the balance rim would carry more weight toward the balance centre and in effect maintain the effective diameter of balance and keep its speed of vibration unchanged. It most be realised that these changes are real, though so infinitesimaL A second factor is that of position, as it affects the running friction through the influ ence of gravity, inertia and friction. These two factors of temperature and position are real, though somewhat intangible. and call for the exercise of the highest skill of the watch maker and constitute what is called 'Adjust ing.' The means for °temperature adjusting' have already been described, and as the proc esses of °position adjustment involve such a variety of delicate manipulations of the balance and its pivots and also of the accompanying hair-Wigs, any attempted description of the process would be useless. It should be said that the obtaining of correct adjustment involves a series of 24-bour trials in the established ex treme variations of 50°, i.e.. between 40° and Fahrenheit, and also in not less than three 'positions' while the highest grades require to be adjusted to five positions.
A watch has been generally understood to mean a small timepiece in portable form, usually to be carried in the pocket. In later years, however, watches have been made in sizes and forms suitable for use as articles of convenience and ornament especially adapted for ladies' wear. One of the triumphs of au tomatic machinery has been the production of watch parts so extremely delicate as to make possible the construction of watch movements so small as to be covered by a dime. On the other extreme of size portable timepieces are made to rem eight days. Movements of this size have come into extensive use on motor cars and as desk watches, etc. Movements of this size are also made of special grade and cased in the form of ship chronometers and are coming into extensive use for navigation, the United States government having hundreds of. them in use.