556 SEC. 10. ELECTRICITY. 



is opposite the printing hammer. The current actuates the printing hammer 

 by releasing a detent in the wheel- work which drives the hammer. 



There is a peculiarity in the electro-magnet which releases the detent. Its 

 cores are polarised by a permanent magnet sufficiently strongly just to retain 

 the armature in contact with its poles. The current overcomes this polarity 

 and releases the armature, which is drawn away by a spring. It is replaced 

 by the wheel- work connected with the hammer. 



1537. Andrews' Relay, for Hughes' Type Printing Instru- 

 ment, 1868, used by the United Kingdom Telegraph Company. 



This relay is adapted for relaying the short currents required for working 

 the Hughes' instrument ; its peculiarity consists in the relayed currents being 

 equal and independent of the line current. 



Series of Apparatus for Recording the Steinheil or Single 

 Needle Code. 



The first recording telegraph was Steinheil's, completed in 1837. The 

 code was formed of dots recorded in two lines, those in one of the lines 

 being formed by the + , those in the other line by the current. The code 

 resembles that of Cooke and Wheatstone's single needle. 



The system, if ever brought into practical use, was superseded by that of 

 Morse, in which the code is comprised of marks of varying lengths. 



But, as the dash occupies thrice the space and thrice the time of a dot, 

 attempts have been made from time to time to introduce apparatus regis- 

 tering the Steinheil or single needle alphabet. 



1564b. Unpolarised Recorder, for registering the single 

 needle code. 



1564c. Unpolarised Recorder, for registering the single 

 needle code. 



1564d. Polarised Recorder, for registering the single 

 needle code. 



1564:6. Polarised Recorder, for registering the single 

 needle code. 



The negative current prints a dot (), the positive current two dots( m \ 



transversely. The first represents the dot, the second the dash of the Morse 

 alphabet. The letter A is written thus . . . . J . 



1564f. Non-polarised Recorder, for registering the single 

 needle code. Richard Herring's system. 



The negative current prints a dot ( R ), the positive current a transverse 

 dashf i J, so that the printing resembles the Morse alphabet. The letter A 



is written thus | . 



1564g. Modification of Wheatstone's Automatic 

 Transmitter, used in connexion with Richard Herring's 

 system. 



1564h. Modification of Wheatstone's Perforator, for 



his automatic system, arranged to punch the single needle code, 

 used in connexion with Richard Herring's system. 



