The almost absolute uniformity in the op. eration of the most improved modern watch making machinery insures a resulting product so uniform in quality and dimensions as to make needless the minute 'fitting' operations which are indispensable in work produced by even the earlier American methods. So ac curately is the work performed that many of the most delicate portions of the watch, whose exact performance is absolutely essential, do not come together until all the finished pans meet for the final assembling.
It may appear strange, but it is neverthe less a fact that, by modern methods, watches are not made by watchmakers, as that term is generally understood, but by machines, by which it is to be understood that the component parts of the watch are all fabricated by ma chines designed for that special use and pur pose. When those individual parts are finished and collected so as to suffice for complete watches they are assembled for the first time and when each part is in its proper place and the watch is 'wound' it is run for a period of one hour, which is sufficient to determine whether it is inclined to run faster or slower than the standard rate. • But when the numer ous portions of the mechanism are made and assembled, the work of the skilled watchmaker begins; for he it is who by means of the• skill and judgment, which are acquired by experi ence, is able to discover the individualities and peccadillos of each movement, and so remove any that its performance shall be satisfactory.
It has already been said that the manufac ture of watches by modern, that is, by Ameri can methods, is a very complex business, in volving the employment of large capital and demanding the highest executive and me chanical talent.
The enormous growth of the railroad busi ness in the United States and the .greatly in creased speed at which trains are now run has made absolutely necessary a standard of time and a high degree of accuracy in the running of all time pieces which are in any way con nected with the running, of trains. These new and exacting requirements are met by high grade watches with special adjustments to position as well as temperature. The natural effect of the requirements of the railroad time service has been to establish a higher of accuracy in rate for watches for the public.
It will be readily comprehended that the• product of a well-designed and properly-made automatic machine will be much more uniform• in its measurements than could be possible with an individual workman, even one• of the highest skill. But the most delicate parts of'
a watch demand a degree of exactness that is impossible of attainment by even the most delicate measurement of mere size. These delicate parts are those which constitute the, `escapement' whose combined function is to control the speed of the entire mechanism. The demand for exactness in the vibrations of the watch balance wheel• which govern time rate allows of no variation whatever— it is positive. To obtain the required number of 18,000 vibrations of the balance per hour two factors are required to operate in proper' co-ordination, viz., the balance wheel and its accompanying hair-spring, the requisite being the proper adaptation of the weight of the balance to the elastic force of the spring. But there are other factors which cannot be ignored in the attempt to secure the precise rate of balance vibration. The first of these is tem perature. It is one of the laws of nature that metals expand under the influence of heat, and it is evident that with a given amount of driving power a large wheel cannot be moved as rapidly as a smaller one. This being the case it must follow that the speed of oscillation of a watch •balance wheel must vary in rapidity as the size of the wheel is modified by the temperature changes which affect it. so that if nothing could be devised to counteract the normal effect of temperature changes, the speed of the mechanism would be constantly changing in conformity to varying tempera-. cures. Fortunately a most ingenious form of construction of the balance wheel has made possible a means of self-correction, by which. the form of the balance is made changeable, so that the expansion or contraction of the metals which compose the balance is so utilised as to maintain the effective diameter practically constant.
The method by which this result is achieved will readily be understood by the help of the accompanying illustrations, in which Figure 1 shows two bars of metal of equal lengths, when at normal temperature. The dotted lines indicate the relative amount of ex pansion of the two metals — steel and brass. Figure 2 shows the two metals joined by fusion. Figure 3 shows the effect of heat upon this bimetallic bar— the greater amount of