An introduction to the study of the Diatomaceae . of theglass. Just in front of the focussing screen a groove shouldbe cut, permitting of tin plates to be used as masks to give aclean edge to the photograph. The most suitable size ofcamera for the above apparatus would be half-plate, 6^ x 4finches. The microscope tube should be of large diameter, unless aprojection ocular is to be used ; its length also is animportant matter, but most opticians are now makingmicroscope stands with a series of draw tubes, which enableone to vary the tube from 6in. to i2in., and to work at anylength that seems t
An introduction to the study of the Diatomaceae . of theglass. Just in front of the focussing screen a groove shouldbe cut, permitting of tin plates to be used as masks to give aclean edge to the photograph. The most suitable size ofcamera for the above apparatus would be half-plate, 6^ x 4finches. The microscope tube should be of large diameter, unless aprojection ocular is to be used ; its length also is animportant matter, but most opticians are now makingmicroscope stands with a series of draw tubes, which enableone to vary the tube from 6in. to i2in., and to work at anylength that seems to give the best results. It is important to see that the inside of the microscopetube is uniformly of a dead black. It is essential that the objectives should be corrected forphotography, that is to say, the visual and chemically actinicfoci must be coincident, or the photographic results will be 62 AN INTRODUCTION TO THE blurred and out of focus. Most opticians supply suitableobjectives. Very good work can be done without an eye-piece, but the. very best can only be accomplished with its aid. It must beclearly understood that the ordinary eye-piece is not adapted STUDY OF THE 63 to photography, and that only those constructed specially forthe purpose must be used. These are fitted with one endrotating in a spiral slot, the use of which is explainedsubsequently. Undoubtedly, a projection ocular is a great convenience,as the camera does not require to be so long, 30m. beingample, and at least two-thirds less than the extensiongenerally required when working without one. It is worthy of note that Zeisss low power compensatingoculars may be used for projection in place of his projectionoculars, with excellent results. The Dark Room. Although development may be carried out in the bedroomat night, in a cupboard, under stairs, in a wine-cellar, andother similar places, they are obviously inconvenient andquite unsuitable for systematic scientific work. A roomshould be fit
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