258 Transactions of the Society. 



this work), a 4^-in. Unar, and a 6-in. Gocrz. I use a / 5 • 6 dia- 

 phragm with the Dallmeyer, that of / 8 with the Unar, and / 8 

 with the Goerz. 



Of course, for low magnifications of a rough object it is 

 advisable to work with a low power — the 4^-in. focus lens was 

 used for most of the prints exhibited — but for larger objects a 

 6-in. lens would define better. The little Dallmeyer lens is a 

 marvel for definition and flatness over the small field used. 



I have had extra tubes made for my Microscope (a Van Heurck 

 by Watson) to take the place of the lower rack work tube and the 

 upper sliding tube, which carry the photo lenses — the Dallmeyer 

 at the bottom of the draw-tube, the Unar (for which I had a new 

 mount made so as to get it inside the tube), about 1^ in. down the 

 tube from the top, and the Goerz outside on the eye-piece end of 

 the Microscope. These adaptations enable the lenses to be carried 

 at the suitable distances from the object on the stage, and allow 

 sufficient rackwork for focusing. When the distance is too great 

 (as it will be in low-power work) for the hand to reach the focusing 

 pinion, I have to use a Hooke's joint focusing rod, but for the 

 higher powers I have a long rod on the other side (the right) of 

 the camera with a pulley wheel near the end, over which and the 

 fine-adjustment screw-head runs a cotton thread-loop, which I find 

 quite effective for monocular work, even with a -^ objective. 



The camera I use is a whole plate one, with a long bellows, and 

 for long-distance work a telescopic attachment in front (made of 

 rolled brown paper). The upright position of the plate in the 

 camera is the more convenient for photographing opaque objects 

 requiring to be lighted from the front and side, and in this case the 

 objective should be divided horizontally. For transparent objects 

 lighted centrally from the back, the plate may be horizontal, and 

 the lens divided vertically. I effect the reversal of the images on 

 the plate — so that the prints will not require to be cut, and so 

 simplify the mounting — by using a carrier in the dark slide (the 

 whole plate slide allows this to be done) in which the plate (5 by 

 4 in.) can be placed 2^ in. out of centre, so as to receive the image 

 from the right hand (or upper) half of the lens on the left hand (or 

 lower) half of the plate. The opening in the carrier should be 

 7| in. by 4 in., a piece of glass 2£ in. by 4 in. filling the otherwise 

 unoccupied end. A screen (of blackened card or thick paper) with 

 an aperture in the centre of 2§- in. by 3 in. should be placed in the 

 carrier, to protect one half of the plate while the other is being 

 exposed. After exposing one side of the plate, the slide is taken 

 into the dark room, and the plate moved to the other end of the 

 carrier. Then the screen on the objective is moved half round (or, 

 in the case of a lens in the draw-tube, the tube is given a semi- 

 revolution without disturbing the focus), and the second exposure 

 can be made. 



