34 



PHOTO-TELEGRAPHY 



i K 



i Adjusting 



Screw 

 M 



short focus lens is provided in the hole nearest the 

 receiving box. The shadow of a magnesium 

 shutter (described later) attached to the wires can 

 be sharply focussed upon a diaphragm by sliding 

 the tube T to the correct position. 



A metal collar (indicated by the 

 dotted circle) is fixed above the 

 pole-pieces into which the moving 

 part of the galvanometer is fitted ; 

 this part is shown separately in 

 Fig. 15. The outside portion of 

 this (MN) is a cylindrical tube 

 which fits into the collar. A sliding 

 piece S is free to move up and 

 down inside the tube, and is fitted 

 with a screw thread, over which a 

 graduated adjusting nut is placed. 

 By turning this regulating screw, S 

 is moved up or down and the 

 tension on the wires varied. The 

 wires, about T^oo^h ^ ncn thick, are 

 attached to two very fine springs (of 



FIG. 15. 



the same material) fitted to S. The small shutter F, 

 about 2 X 1*5 mm. in area, and as thin as possible, is 

 gummed to the wires so that it comes on the optic 

 axis when the piece is fitted into the magnet collar. 

 The sliding portion S is insulated from the brass 

 tube, but is connected with a contact K. This con- 

 tact and another metal button C fit against two 



