394 



NATURE 



\ August 25, 1887 



takes up with the set-hands wheels. In Fig. 5, which we 

 shall refer to again further on, this arrangement can be 

 readily perceived. 



To understand repeating work — in which a good deal 

 of progress has been made — it will be as well at first to 

 refer to Fig. 6, which shows the mechanism of a clock 

 chiming the quarters. On the left will be seen an anchor- 

 shaped piece with teeth in it, called a " rack." At the 

 foot of the rack will be seen a star wheel carrying a piece 

 in form similar to a snail. This piece is called the 



" snail," and it has twelve gradations corresponding to 

 the twelve hours. On the right will be seen another rack 

 and snail which do duty for the four quarters. Both the 

 quarter and hour racks are at present held free of their 

 respective snails by the hooks shown in the diagram. 

 The method of action is as follows : — At each hour the 

 quarter rack, by means of mechanism connected with the 

 going train of the clock, gets itself liberated from the hook 

 and falls upon its snail. The distance through which it 

 falls is determined by the depth of the depression in the 



Fig. 



-Hour Enj Quarter striking raechanisra. 



snail which is opposite to it. The quarter train having 

 also got freed at the same time, proceeds to run, and 

 winds up the rack again in doing so. The distance 

 through which the rack has fallen determines the length 

 of time the quarter train runs, and consequently the length 

 of the chime. In falling the quarter rack also discharges 

 the hour rack. The hour train is held until the quarters are 

 finished ; at their conclusion the hour rack is wound up 

 by the hour train through the distance it has fallen 

 which depends upon the depth of depression in its snail 



opposite to it), and the number of the hour struck is in 

 proportion. 



The light which the foregoing throws upon repeating 

 work is with regard to the snail and rack arrangement. 

 When you move the slide of a repeating watch you do two 

 things. You wind up the main-spring, which actuates the 

 repeating train, and the extent to which you are able to 

 do so depends upon the depth of the depression in the 

 snail which is opposite to the piece which you are 

 moving. When you reach the bottom and press against 



