On some Modifications of Recording Apparatus. 353 



light French clock pendulum suspension. Each suspension 

 is pierced by a fine screw tipped with platinum. These 

 screws are so adjusted as just to touch the surface of the 

 block at each swing of the pendulum. One pole of a 

 bichrome battery is connected to tlie works of the clock. 

 The current, passing down the pendulum, passes along the 

 screw in contact and on to the time-marker, with one end of 

 the magnet of which the screws are connected. The other end 

 of the magnet is connected to the other pole of the battery. 



The contacts are in metallic connection by wires leading 

 to a binding screw on the side of the clock. But a key 

 interposed can be employed to break the circuit, in which 

 case the pendulum only makes circuit on one side of its 

 swing. Thus it will send second-signals to the marker; 

 when both are connected, half-second signals will be sent. 

 The connections are obvious from the diagram. 



It is often necessary to keep accurate record of periods of 

 the time during which an observation is to be made. Periods 

 of five minutes or upwards can be readily noted from a watch 

 or ordinary clock with sufficient accuracy, but shorter periods 

 of a minute or less cannot be so readily observed without 

 the aid of a special assistant. To provide for this, I have 

 made an addition to the clock referred to, which answers the 

 purpose well. 



To the end of the arbor of the scape wheel in the clock 

 just described, a small steel claw is fixed, which will thus 

 revolve once in fifteen seconds. At one point of its revolu- 

 tion it touches and closes a platman contact carried on a 

 light steel spring. This momentary contact serves to energise 

 a small electric bell connected with it, and placed on the 

 experimental table. Thus every period of fifteen seconds is 

 indicated by a stroke of the bell. Another wheel of the 

 train makes one revolution in two minutes, and a similar 

 contact is adapted to its arbor, and communicates with the 

 magnet of another but larger bell set on the same stand. By 

 counting the strokes of the two bells, periods of time from 

 fifteen seconds and upwards can be readily noted without 

 lifting the eyes from the table. This clock is made by 

 Mr Bryson, George IV. Bridge. 



