LINE PHOTOGRAPHS 101 



dot running into next, so that the whole surface 

 of the paper was discoloured and all the details of 

 the image hopelessly intermingled. I then in- 

 creased the capacity of the condenser in the line 

 balancer, and the photographs were also tempo- 

 rarily made with a coarse line screen (30 to the 

 inch), and the quality was at once better. A great 

 deal depends, needless to say, on the quality of the 

 half-tone photographs, which require quite a par- 

 ticular method. of preparation. 



The method of making these photographs is as 

 follows : The picture to be telegraphed is pinned 

 flat to a board or placed in a frame with glass 

 over it, and fixed vertically in a copying apparatus. 

 It is usually illuminated with an arc lamp at 

 either side with reflectors. The camera used for 

 copying it has a half -tone screen fixed at a certain 

 distance in front of the sensitive plate. This 

 screen consists of a glass plate ruled with a certain 

 number of lines to the inch ; thirty or thirty-five 

 lines to the inch is known as a " coarse " screen, 

 the number for high-class illustrations, printed on 

 surfaced paper, being 120 upwards to the inch. 

 Usually two such screens are used, crossed so that 

 the rulings are at an angle of 90 to each other, and 

 then the picture is broken up into dots ; but it can 

 easily be seen that where the picture is put on a 

 cylinder and travels round beneath a tracing point, 

 lines are preferable to dots ; the lines of course lie 



