Page:The New International Encyclopædia 1st ed. v. 20.djvu/398

WATCH. 330 WATCH. keeper possible. The first watches were made very early in the sixteenth century, Peter Hele, a "clock-maker of Nuremberg, being usually credited with the invention. At first a straight spring was used, but this was soon replaced by a coiled spring. The first balance used in watches, termed a foliot, corresponded in its action to the suspended weights on a horizontal lever of an early clock. It consisted of a metallic rod ter- minating at each end in a heavy mass, the whole formed out of a single piece of metal. This was afterwards replaced by a wheel, in which the weight, accumulated mainlj' on the rim, took the place of the weights suspended on the ends of a bar. The first great improvement made in watch construction was the application of the coiled hair-spring to the balance-wheel. This invention was probably made by Hooke about 16.58. The earliest watches had little physical re- semblance to their modern successors. One of the first was a cylindrical box of metal, chased and gilded, the lid pierced with an opening over each hour mark through which the hand could be seen. Others were made in many grotesque shapes and in all sizes from the diameter of a saucer to that of an ordinary lead pencil. Curi- ous mechanism was as much prized as quaint form in these early timekeepers, and both seem to have been considered of more importance than the accurate measurement of time. Alarm watches, and repeaters, or striking watches, were great favorites. The earliest watches usually had but one hand. Enamel dials were first used in 1650. Jewels were first used as pivot bear- ings for watches about 1700. The fusee, which was invented early in the sixteenth century, continued to be used in Eng- lish watches until toward the close of the nine- teenth century, although it had been discarded in the American niachine-made watch many years before. The fusee is a spirally grooved cone, connected with the barrel which contains the main-spring by a chain, one end of which is fixed to the broadest part of the cone and the other end to the barrel. From the fusee the mo- tion was communicated to the train, and the theory of its use was that in its unwinding it corrected the variations in the force of the main- spring and so equalized the power exerted upon the train. The equalizing efl'ect is due to the fact that, when the spring is all coiled up and its force upon the barrel is greatest, the chain is acting upon the small end of the fusee and its leverage upon the fusee is least; but as the force of the spring diminishes, the chain having readied a broader ]iart of the fusee, the leverage is increased, and tlip two are so adjusted to each other that the action of the spring modified by the leverage of the chain produces a uniform stress in the fusee. In most modern watches the great wheel forms part of the barrel and the diminishing power of the mainspring, as it un- coils, is neutralized by the escapement, with which the balance-wheel is connected. The later models of watch movements made by the Ameri- can Waltbam Watch Company are constructed with what may be properly designated as a 'de- tached barrel' — a method which gives greater strength to the barrel (of steel, instead of brass) and constitutes a safeguard against the breakage of the main-spring Almost immeiliately after the invention of the hair-spring attempts began to be made to in- troduce into watches an escapement which would produce greater accuracy than the vertical es- capement at first used. The detached lever es- capement described farther on is now commonly used in watches. Early in the history of both clock and watch construction it was noticed that variations in the temperature produced varia- tions in the rate of going, the increase or diminu- tion of the temperature affecting to some e.xtcnt the moment of inertia of the balance-wheel and to a great extent the elastic force of the balance- spring. A rise in the temperature makes the balance expand, and therefore augments its mo- ment of inertia ; it adds to the length of the spring, and thereby diminishes its elasticitj', the elastic force of a spring varying inversely as its length; and the time of vibration of the balance, which depends upon the moment of inertia di- rectly and upon the elastic force of the spring inversely, is increased — that is. the watch goes more slowly — in consequence both of the increase of inertia and of the diminution of the elastic force of the spring. A fall in temperature is at- tended by opposite results, the watch going more rapidly. The importance of discovering some means for correcting these temperature varia- tions was most evident in connection with marine chronometers, upon which navigators depend for reckoning their longitude at sea. Early in the eighteenth century John Harrison, who in- vented the gridiron pendulum for clocks and sev- eral other improvements in their mechanism, made the compensating balance, which was soon applied not only to chronometers, but to all high- grade watches. In the compensating balance, the balance-wheel is made of two metals — brass and steel — which are affected at unequal rates by temperature. The outer rim is of brass and the inner rim and cross arms of steel, the two metals being firmly united by fusion. To allow for an expansion, the wheel is made in two equal parts, joined by means of a cross arm as shown in Fig. 1. The increased expansive and contractile power of brass over steel is so utilized by pro- portioning in this combination of the two metals that the changing size of the balance-wheel auto- matically adjusts itself to the varj'ing condi- tions of the hair-spring. It will be noticed (Fig. 1 ) that the balance-wheel is ballasted with tiny screws. Their object is twofold, to adjust the balance-wheel to the exact weight required to make the desired number of vibrations — 18.- 000 per hour — and, by changing the positions of the screws, to adjust the effective weight of the balance-wheel on the diameter to meet changing conditions of temperature. Recent improvements ill watch mechanism have been directed toward constructing a movement that shall not be af- fected by electrical disturbances. In order to ac- complish this, the balance, roller, hair-spring, pallet, and fork are made of non-magnetic ma- terials. Briefly summarizing the steps by which the iii('<'hanism of the modern watch has been de- veloped from I)e 'ick's model, we find: (1) The use of the spring as motive force: (2) substitu- tion of balan<'e-wlice1, with hair-sining. for weights; (3) successive improvements in es- capement: (4) introduction of enamel dials; (5) introduction of jewels as pivot bearings: (6) invention of compensating balance; (7) dis-