484 



NATURE 



[Sept. 22, 1887 



FIFTY YEARS' PROGRESS IN CLOCKS AND 

 WA TCHES. 1 



II. 



TO pass on to another phase of mechanical improve- 

 ment, a wonderful advance in the mechanism of 

 chronographic watch-work has been made during the 

 period we refer to. In this department the first chrono- 

 graphs to be introduced were those having a kind of 

 double hand, the lower portion of which carried a tiny 

 vessel of ink. When an observation was requisite, the 

 upper part of the hand passed through a small orifice in 

 this ink-vessel, marking a dot upon the dial below. We 

 have had of late years, however, much cleaner and more 

 convenient arrangements. The most usual form is as fol- 

 lows. In addition to the ordinaryminute and r^«/r^-seconds 

 hands there are auxiliary hands, which always stand at 

 zero when not moving. Pressure on the crown-piece 



sets them going, a second pressure stops them, and the 

 third pressure sends them back to zero ; and it is inter- 

 esting to observe that they always return to zero — their 

 normal position — the shortest way round the dial. The 

 nature of the mechanism by which these operations are 

 effected is briefly as follows. Pressure on the crown- 

 piece causes a wheel carrying different sets of cams 

 to advance step by step. These cams, which correspond 

 to the starting, stopping, and returning of the hands, 

 operate on springs and levers. The first motion frees 

 the auxiliary hands, and also throws them into gear with 

 the watch-train. The second motion throws them out of 

 gear and clutches them so that they shall not shift. The 

 third motion sends them back to zero, and this is effected 

 in the case of both by what is called a heart-piece. This 

 heart-piece, as regards the seconds-hand, is shown in 

 outline at the centre of Fig. 8,^ which has already appeared 

 as Fig. 5 in the first article. It is to be mentioned 



Fig. 8. — Chronograph with Swiss Keyless work. 



that the heart-pieces go round with their respective hands. 

 The third pressure releases the clutches and also causes 

 the lever, shown above the heart, to descend upon it ; the 

 heart and hand being now free to move, the lever draws 

 round the heart until it finds the lowest position of it, 

 which, as is natural, is arranged to correspond to the 

 normal position of the hand. The gearing-wheels and 

 clutch-levers can be very well seen in Fig. 9. 



In another form of chronograph a long seconds-hand 

 is superimposed over another so as to appear as one with 

 it. They both travel with the watch-train ; until a first 

 pressure stops one, and a second pressure the other ; the 

 interval between the two pressures can now be read off 

 at leisure. A third pressure sends them flying to the 

 place where they would have been if they had not been 

 stopped at all, even should they have been kept standing 



^ Continued from p; 395. 



for a week. They, also, always return the shortest way. 

 The mechanical arrangements consist of a heart-piece 

 for bringing the hands together, and they achieve the 

 position where they would have been had they not been 

 stopped by means of a kind of cylinder sliced through at 

 an angle not perpendicular to its axis. Whilst the hands 

 are travelling, the faces where the cylinder is cut are kept 

 pressed together by springs, but they are parted when the 

 hands are brought to rest. One half of the cylinder goes 

 on with the watch-train, the other half (in connexion 

 with the hands) remains suspended above it ; at the third 

 pressure of the crown-piece the top half is permitted to 

 descend, when it naturally seeks its former position with 



' We are indebted to Mr. Britten for the use of Figs. 5, 9, 10, 11, 12, and 

 15, and to Mr. Glasgow and the Messrs. Cassell for Figs. 13 and 14. Readers 

 who wish further insight into the details of our subject should consult both 

 Mr. Britten's and Mr. Glasgow's books. 



