II. TO pass on to another phase of mechanical improvement, a wonderful advance in the mechanism of chronographic watch-work has been made during the period we refer to. In this department the first chronographs 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 follows. In addition to the ordinary minute and centre-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 interesting 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. 8,1 which has already appeared as Fig. 5 in the first article. It is to be mentioned 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.