358 SEC. 10. ELECTRICITY. 



1572. Siemens 9 Relay used with the ink-writer. 



1563. Stroh's Polarised Belay , with Inducing Magnet. 



This relay is similar in construction to the electrical portion of the Wheat- 

 stone " Receiver," No. 1557. 



1564. New form of Non-polarised Relay. 



This consists of two vertical electro-magnetic bobbins the cores of which are 

 prolonged. Two soft iron needles are fixed on. a vertical axle passing between 

 the coils, one at the top and one at the bottom end of the axle. These 

 needles are placed crosswise, so that when the cores are rendered magnetic the 

 four poles of the bobbins tend to turn the needles on their vertical axis in the 

 same direction. Two adjustments are provided, one the ordinary spring 

 adjustment, the other for moving the needles nearer to or further from the 

 poles. 



This arrangement is much more sensitive than the old form of non-polarised 

 relay with horseshoe electro-magnet and annature. 



1566. Double Current Translator, used for relaying 

 double current Morse signals. 



The signals are relayed from the lever of the sounder, the latter being worked 

 by a polarised relay in the line circuit. The necessary alterations to the 

 connexions for restoring the apparatus to its normal condition when trans- 

 mission in either direction has ceased is accomplished by an automatic switch 

 called a " spacer," which consists of an electro-magnet, armature, lever, and 

 stops. The local circuit of this magnet is closed by the relay which works 

 the sounder when a marking current is sent, and by another relay placed in 

 the line circuit when a spacing current is sent, so that the a-rmature is con- 

 tinually held down while a station is sending. 



The armature is prevented from rising during the short interval between the 

 currents by a " shunt " placed across the terminals of the electro-magnet 

 coil, which forms a path for the extra current direct when the local circuit 

 is broken, and delays the demagnetisation of the iron core. 



1567. Duplex Translator for relaying the signals on long 

 circuits, worked on the duplex system. 



This apparatus consists of two sets of duplex instruments combined. 



1569. Testing-Box Galvanometer. 



Used for testing wires ; the requisite changes of connexions for receiving 

 and sending currents are made by a peg switch in front of the instrument. 



153O. Switches or Commutators for making Changes 

 of Wires in Circuits. 



a. Earliest switch for double needle, fixed at Norman ton about 1857. 



b. Tumbler switch. 



c. Umschalter or Universal switch. 



1555. Wheatstone's Automatic Telegraph, 1867, 

 The Perforator for preparing the paper ribbon. 



There are three punches. The centre punch perforates small holes in the 

 centre of the ribbon, which form a rack by which the paper is carried? orward 

 in the transmitter. The centre lever acts on this punch only ; the other two 



