I 48 PRACTICAL PHOTO-MICROGRAPHY. 
arrangements between lantern and sensitive paper; but 
the lantern should either be placed in a box or so fitted 
that no light escapes from it to fog the paper. The 
front of the lantern should have a stretch at least half 
as long again as the focal length of the lens, and a lens 
of moderately short focus should be used, say three- 
and-a-half or four inches. The negative must be 
evenly lighted, and if any difficulty is found in arranging 
this, a piece of ground-glass may be put inside the 
lantern between light and condenser; but this necessity 
should not arise. The “ Cantilever ” apparatus of 
Hume, of Edinburgh, is a good example of enlarging 
apparatus, but a short-focus lens should be fitted to it 
(fig. 34). To give an idea of the stretches that may 
be required, we may state that, with a lens of four 
inches equivalent focus, to enlarge two diameters we re¬ 
quire Y, three diameters , four diameter \° inches, 
the numerator giving distance from lens-centre to 
sensitive surface, the denominator the distance from 
lens-centre to negative. 
Exposure follows here the same rules as for contact¬ 
printing on bromide paper; but, if desired, a more 
