44 



PHOTO-TELEGRAPHY 



to prevent vibration. In many later models of 

 photo - telegraphic apparatus the motors are 

 mounted on separate stands and connected to the 

 driving gear by flexible shafting. 



The relay used by Professor Korn for utilising 

 the synchronising current to close the magnetic 



FIG. 21. 



check release circuit is a Siemens & Halske polar- 

 ised relay. A polarised relay is not necessary 

 unless it be sufficiently sensitive to work with 

 a current equal in intensity to the line current for 

 the galvanometer. The Siemens & Halske relay 

 can be rendered more or less sensitive at will by 

 regulating the distance of one magnet from the 

 armature it has to attract, keeping the other 

 magnet fixed. 



