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The principles upon which this beautiful art was founded might be read in 

 any of the many manuals on photography, and which were published at a 

 cheap rate ; therefore, leaving those, he would pass on to the practice. If 

 anyone needed to learn about the various apparatus employed for photo- 

 micrography, full particulars would be found in Beale's " How to Work with 

 the Microscope," and in Cutters' " Microscopical Technology," both of which 

 works were in the Club library. 



In the first place he claimed for his plan great simplicity, being, as could 

 be seen, nothing more than a lidless box placed on its side. At the left end 

 it had a' square hole, but any aperture would do. A brass plate, having an 

 adapter in it, slid in and out on runners for more easily changing the powers 

 when it was desired to do so. Another aperture was made at the top, and 

 covered by a blac! etied chimney to carry off the heat from the duplex paraffin 

 lamp inside. Another aperture at the bottom of the right side served to 

 admit the air to the lamp when the front of the box was covered up by the 

 black focussing cloth ; within the box, and attached to the left side, was a 

 carrier working on a long and fine screw, which served to adjust the object to 

 the correct focus. Two condensing lenses, one to render the rays of the lamp 

 parallel, and the other to condense them on the object, completed the arrange- 

 ment as far as the box was concerned. The light passing from these through 

 the objective emerged as a cone, and on the principle of a magic lantern 

 projected the image on a screen to the left of the operator. 



The screen consisted of a heavy piece of wood, having a groove formed in 

 it, and carrying another block upon which the screen was held. The screen 

 which received the image might be made of an oblong piece of glass, either 

 four and a -quarter inches by three and a-quarter inches, called by photo- 

 graphers a quarter plate, or by a plate 5x4, according to the amplification 

 it was desired to employ, or as the nature of the object might indicate, or, if 

 lantern slides were desired, on a square three and a quarter inches. These 

 should have a piece of smooth writing paper gummed on that surface pre- 

 sented to the image. The image being then thrown on to the screen, and 

 the hand placed under the focussing cloth, the carrier must be moved by 

 means of the screw adjustment until the image of the object was sharply de- 

 fined on the screen. 



In many writings on the subject it was stated that the actinic and 

 visual foci of microscopical objectives were not coincident. All he could say 

 was that with the one-third of an inch, which he was about to employ, and 

 with Zeiss's'D, no alteration was needed from the visual focus. The screen 

 might then be removed and its place occupied by a dry gelatine plate, and 

 the exposure accurately timed according to the nature of the object ; but 

 only experiments could determine that. Care must be taken before making 

 the exposure that the light through the objective was cut off till the plate 

 was in position, when it might be allowed to fall on the plate for the requi- 

 site time, and then cut off again before removing the plate to the developing 

 dish, this was obviously necessary to avoid blurring the image. It was need- 

 less to say that the only outside light must be a non-actinic red light, and no 

 ray of white light must be allowed to reach the plate or it would be <; fogged " 

 — that was to say, when it was developed it 'would be veiled by a misty de- 



