KORN'S TRANSMITTER 25 



on to the glass cylinder CO', so that the rays cross 

 at the point A where the pencil meets the first 

 surface of the cylinder. A transparent photograph 

 printed on a celluloid or gelatine film is wrapped 

 round the cylinder, so that at A the light passes 

 through one small point of it ; it travels thence 

 into the 45 prism P, by which it is reflected 

 upwards upon a selenium cell SE. The glass 

 cylinder is attached to a shaft with a screw thread, 

 which turns in a fixed threaded collar T, so that 

 when revolved by a motor it rises and turns spirally. 

 It is thus seen that the spot of light at A in effect 

 traces a spiral path over practically the whole 

 photograph in due course. The intensity of the 

 light at any instant depends on the density of the 

 photographic film in the portion traversed at that 

 instant, so that the light falling upon the selenium 

 cell is always varying in accordance with the density 

 of the photograph. 



The " point " embraced by the light pencil at A 

 is in reality about 3X2 mm. in area, hence no 

 small details can be transmitted as several would 

 be embraced at once by the beam. This is the 

 reason why only portraits or very simple subjects 

 could be transmitted by the selenium machines.* 



* More complicated pictures have been transmitted by 

 Korn's selenium machine by enlarging up the subject and 

 dividing it into three or four parts, telegraphing each separ- 

 ately and then joining up the telegraphed components. 



