360 SEC. 10. ELECTRICITY. 



About 20 seconds before 1.0 p.m. a local current sent from the clock 

 actuates this switch, causing the levers to be shifted from the stops which are 

 m connexion with the ordinary instruments to those connected with the 

 relay which fires the gun. When the time current passes through the relay 

 it closes a local circuit in which the gun fuze and the battery are included. 



About 20 seconds after the time current has passed, the local current 

 actuating the electro-magnetic switch is interrupted by the clock, and the 

 levers of the switch to which the line wires are attached are again placed in 

 connexion with their respective 'instruments. 



The clock itself is corrected daily in the following way : 



It is kept at a slightly gaining rate, and is stopped automatically by a 

 detent which acts on a pin projecting from the escape-wheel when the hands 

 point to 1.0 p.m. The pendulum, however, continues swinging. 



When the time-current is received the outgoing current from the time-relay 

 passes through an electro-magnet inside the clock which liberates the detent. 



The clock is so arranged that a second electro-magnetic switch may be 

 actuated, and the time current distributed in a similar way at 10.0 a.m. 



1571. Automatic Time-Switch for switching line-wires from 

 their instruments and connecting them to the time-relay. 



1573. Galvanometer for showing incoming time-current. 



1574. Galvanometer for showing outgoing time-current. 



1553. Early form of " Chronofer," or time-current 

 sending apparatus, used in London about 1852. (Incomplete.) 



1575. Lightning Protectors or Dischargers (various). 



a. Varley's Lightning Protector (original form). 



b. 



/. 



i. 



k. 



I 



m. 



n. 



Varley's vacuum (modern form). Tube 



protector, vacuum tubes in water-tight 



compartment far outdoor use. 



Latest form of fine wire protector, Post 



Office pattern, consisting of a metallic bobbin, electro-nickel plated, in con- 

 nexion with the earth. It is wound with a fine wire covered with silk and passed 

 through melted paraffin wax, the wire being placed in the line circuit. The 

 metallic bobbin is carefully lacquered to secure insulation in damp situations. 



1576. Insulators. Various. 

 Original ring insulator. 

 Cone insulator, original form (1845). 

 later 



form for replacing broken insulators. 

 Walker's double-cone insulator (brown). 

 (white). 



Insulator (1847), in which the bolt by which the wire is suspended is in- 

 sulated by mastic cement in the cavity at the top of the insulator. 



