ENLARGING 233 



bellows. Focussing is carried out on the ground glass. 

 Alternatively a large and a small camera can be used 

 together for this purpose. Daylight can be used if 

 desired for enlarging by pointing the camera towards a 

 white reflector or tilting it towards the sky. 



The process in brief is as follows. The apparatus is 

 set up, and the disc of light projected on the screen care- 

 fully examined, and any unevenness corrected by moving 

 the radiant. The negative is inserted in its carrier, and 

 the distances between the lens and negative on one hand, 

 and lens and screen on the other, adjusted to give the 

 desired magnification, and the image carefully focussed. 

 The bromide paper is placed in the dark slide or pinned 

 to the easel, after covering the lens with a shutter or 

 piece of red glass, and exposure given. Trials can be 

 made on a strip of the paper previously, if exposure is 

 uncertain ; it will vary from a few seconds to several 

 minutes, according to the illuminant, density of negative, 

 speed of paper, and scale of enlargement. Development 

 is carried on as usual for bromide papers, except that it 

 is well with large sheets to soak the paper in water for a 

 few moments before pouring the developer over it. A 

 smooth, vigorous paper gives the best results for photo- 

 micrography. Moderately short-focus anastigmats, up 

 to say 1", are the best lenses to use : the 3" micro- 

 anastigmats are suitable if only part of the negative is 

 required to be enlarged, but will not cover the whole of a 

 quarter-plate. The distances required between the nega- 

 tive and lens, and between the lens and bromide paper, 

 in order to get any desired enlargement are given on 

 page 276 for lenses of moderate focal length. 



Lantern Slides. The use of photomicrographs for 

 teaching and lecturing is becoming so widespread, that 

 a brief outline of the process of lantern-slide making is 

 not out of place here. Lantern plates are coated with 

 emulsions similar to those used on bromide and gaslight 



