ground-glass focussing screen, the centre of which is ruled in small squares of half an inch with lead pencil, and then varnished with crystal varnish for a space of about the size of a quarter-plate; this is used with a compound focusser for obtaining microscopically sharp enlargements. The ground side of the glass is next to the plate-glass, and consequently facing the lens, just as in an ordinary camera; the ground-glass is held, at the sides by two small studs, as used for the interior of dark slides. The printing frame fits into a specially made stand, which runs on a couple of parallel pieces of wood on the table, and is instantly clamped at about the right distance from the lens by lever cams, fine focussing being adjusted by means of a short rack and pinion. The above arrangement is, of course, a little more elaborate than actually required, as a printing frame supported in any way so as to be absolutely steady when placed upright, and also parallel with the negative, is sufficient. What is the best lens for enlarging ? is a question we often see asked. Well, the answer is very easy - viz., that lens which took the negative. But this answer requires a little modification. If the negative to be enlarged is a portrait, then a portrait lens may be used; but the back lens of the combination must be placed next to the negative. The most useful lens is undoubtedly the doublet of the rapid rectilinear type, as it gives, as a rule, excellent marginal definition. A single or landscape lens may also be used, but from the necessity of using a smaller diaphragm it is obviously slow.
Apparatus for Enlarging by Artificial Light.
To most amateurs, especially those engaged in business during the hours of daylight, artificial light is the only one they can employ for enlarging; hence considerable attention will be paid to this. We, first of all, as already suggested, divide our lights into petroleum, or mineral oil, gas, enriched gas, limelight, mag-nesium, and the electric light; and we shall endeavour to describe the arrangements for all, but must premise that the first essentials for successful work are that the light, no matter what kind it is, must be, first, small in dimensions, and, secondly, actinic in quality; the first gives greater sharpness, the latter short exposures.
Mineral Oil Lamps. Opinions differ as to the best form of lamp for enlarging, most, if not all, commercial apparatus being