64 ELEMENTARY PHOTO-MICROGRAPHY. 



right position opposite the centre. The dry plate 

 is then put on and covered with a wood block the 

 same size, which again is pressed by a snring to 

 keep the negative and plate in contact. 



The exposure varies with the plate used. " Ilford 

 Special" lantern plates for warm and cold tones 

 require twenty seconds at eighteen inches from an 

 ordinary gas bat's-wing burner. " Ilford Alpha," 

 for red and brown tones, two minutes at six inches 

 from a fish-tail burner. Development and fixing are 

 the same as fo<r negatives. The least fogging of 

 the lights, it should be noted, will spoil the slide, 

 and the image must stand out well defined on a 

 perfectly transparent background. Spoiled plates 

 make good cover glasses, if stripped of gelatine by 

 steeping in boiling water and soda. When the 

 plates are ready for mounting, a square or circular 

 mask is placed between the cover and picture. If 

 there is room on the margin of the mask, which is 

 usually black, the title may be written upon it with 

 white ink, not forgetting to put a white spot in 

 each top corner when looking at the picture the 

 right way about. These are for the guidance of the 

 lanternist who puts the slide into the lantern up- 

 side down with the spots towards the condenser. 

 Nothing is more awkward for both audience and 

 operator than pictures projected in a wrong 

 position. 



