138 THE ELECTRIC TELEGRAPH. 



ing station, from the insulated point, and closes the local 

 circuit so long as the key is held down, and no negative 

 current induced by letting the key go back to its position of 

 rest. 



85. Siemens and Halske's Polarised Ink Recorder. A novel 

 and very useful invention, where the attention of the employe 

 is not invariably to be relied on, or he is occupied with other 

 duties besides his instrument, was introduced by Messrs. 

 Siemens and Halske, in the construction of their polarised 

 ink recorder, in making the clockwork which is used to 

 unwind the paper strip, self- starting. That is to say, as 

 soon as a current arrives, and so long as it lasts, the clock- 

 work is allowed to run and to draw the paper strip over the 

 knife edge of the printing lever underneath the printing 

 disc ; but when the signals stop, the clockwork is arrested also. 



In principle the electro-magnet is the same as that of the 

 polarised relay described above. A strong angular permanent 

 steel magnet polarises the two cores of an electro-magnet, 

 which partake both of north polarity ; while between their 

 ends, the printing beam of soft iron, moving on an axis in 

 the other end of the permanent magnet, has the opposite 

 polarity. 



The clockwork does not in any material point differ from 

 that of the ordinary instruments. A hollow drum is turned 

 by means of a mainspring in its interior, which also puts in 

 motion the entire train of wheels, as well as the printing and 

 driving rollers. A fly regulates the motion of the whole. 



The self-starting apparatus is arranged as follows : Close 

 to the electro-magnet of the printing lever is. a smaller 

 electro-magnet, A B, Fig. 77, called the releasing magnet, 

 the coils of which are in the same circuit as those of the 

 larger one. When a current passes, therefore, through, both 

 their armatures are attracted at the same instant. The 

 armature c of the releasing magnet is carried by the releasing 

 beam, turning on the axis H. At the other end of the 

 releasing beam is a friction spring, o E, which, when the 

 armature is in its position of rest, presses upon the ivory 

 break- wheel F by means of a weight. The last wheel of the 



