754 



SCIENTIFIC RECREATIONS. 



We can see nothing but a crystal dial, perfectly transparent, upon the 

 surface of which two " hands " move, as upon an ordinary clock face. There 

 is no machinery visible, and electricity may be credited with the motive 

 power, because the dial is suspended by two wires. But they will soon be 

 perceived not to be connected with the hands, and all search for the 

 mechanism will be fruitless. 



The hands, moreover, turn backwards or forwards, and may be moved 

 by a treacherous ringer, but will always return as by a balanced motion to 

 their position, not the hour which they were at, but to the time which it 

 actually is. They will take their proper place notwithstanding all efforts to 



Fig. 88 1. M. Robert's clock. 



the contrary, and will then, if let alone, indicate the time as steadily as 



ever. 



i The hands of this very mysterious timepiece carry their own motive 



power, and consist of unequally balanced levers, so to speak, in which the 



clockwork arrangement is intended to disturb the equilibrium. This property 



is employed to indicate the hour and the minute, as we will attempt to 



show. 



The minute hand is the balance, and it is very exactly poised. In the 

 round box fitted to the end of this hand a plate of platinum is displaced by 

 clockwork. The centre of gravity being displaced every instant by the 

 revolution of the weight which goes round once in an hour, the minute 



