308 SEC. 10. - ELECTRICITY. 



signals sent out depend entirely on the interval of time separating two 

 reversals ; the back row of holes controls the marking, and the front row the 

 spacing currents. 



A dot is made by a marking current followed immediately by a spacing one. 



A dash is made by a marking current followed by a spacing current sent 

 after a longer interval. 



For instance, the letter A which is made up of a dot and dash ( . - ) 

 is perforated thus: 



A..C 



When the back pin passes through the hole A it allows . a marking current 

 to be sent, and the printing disc of the receiver at the distant station is brought 

 against the paper ribbon, but immediately afterwards when the back pin falls 

 the front pin rises through the hole B, allowing a spacing current to be sent, 

 which moves the marking disc away from the paper upon which a dot has 

 been made. The dash is made in a precisely similar way ; the back pin rising 

 through the hole C allows a marking current to be sent, and following it at a 

 greater interval than in the case of the dot a spacing current is allowed to be 

 sent by the front pin rising through the hole D, causing a longer mark to be 

 made on the receiving ribbon. 



The great difference between this and the earlier systems is, that the 

 contacts are not made through the paper, but are controlled by the perforations. 



The instrument is arranged to send either intermittent, permanent, or 

 compensated currents. 



By intermittent currents is' meant that currents are sent only at the com- 

 mencement and termination of a signal. 



In using permanent currents, the latter, whether marking or spacing, are 

 continuous for the whole length of the signals, and for the intervals between 

 them, as if a double current Morse key was used. 



By compensated currents is meant that the latter are continuous, as in the 

 last case, but the first portion only of the currents, whether marking or 

 spacing, is sent of the full strength, as during the remainder of a dash or 

 space a high resistance is inserted automatically between the battery and the 

 line, the current being weakened proportionally. 



1557. Wheatstone's Receiver, 1867. 



This instrument is used for recording the signals in Wheatstone's automatic 

 system ; it is simply a sensitive direct ink writer. 



The electrical portion consists of two vertical electro-magnetic bobbins, the 

 iron cores of which are furnished with pole pieces, Two soft iron pieces 

 or tongues are fixed on a vertical axle, and are magnetised by induction from 

 a, horseshoe magnet placed near them ; they play between the pole pieces of 

 the electro-magnet. The marking disc is in connexion with an arm attached 

 to the vertical axle, and is pressed against or removed from the paper ribbon 

 according as the current passes in one direction or the other through the coils. 

 The tongues of the electro-magnets are set neutral, so that they remain on 

 the one side or the other after the current which has moved them has ceased 

 to act 



The speed of the wheelwork can be regulated at pleasure to suit the 

 rapidity of the signals. 



1558. Steinen's Direct Writing Morse Inker, with 

 Morse Signalling Key and Galvanometer. 



