i8S3.] 



MICROSCOPICAL JOURNAL. 



83 



various apparatus employed for photo- 

 micrography, full particulars will be 

 found in Beal's '" How to Work with 

 the Microscope," and in Cutter's " Mi- 

 croscopical Technology," both of which 

 works are in our library. 



In the first place, I claim for my plan 

 its great simplicity, being as you see, 

 (fig. 16) nothing more than a lidless box 

 placed on its side. At the left end it 

 has a square hole ; but any aperture 

 will do. A brass plate, having an 

 adapter in it, slids in and out on 

 runners for more easily changing the 

 powers when it is desired to do so. 

 Another long aperture is made at the 

 top side, covered by a blackened 

 chimney to carry off the heat from the 

 duplex paraffin lamp inside. Another 

 aperture at the bottom of the right 

 side serves to admit the air to the 

 lamp when the front of the box is 

 covered up by the black focussing- 

 clotli ; within the box, and attached 

 to the left side, is a carrier working 

 on a long and fine screw, which serves 

 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 — complete the arrange- 

 ment as far as the box is concerned. 

 The light passing from these through 

 the objective emerges as a cone, and 

 on the principle of a magic lantern 

 projects the image on a screen to the 

 left of the operator. 



The screen consists of a heavy piece 

 of wood having a groove formed in it, 

 and carrying another block upon 

 which the screen is held. The screen 

 which receives the image may be 

 made of an oblong piece of glass 

 either four and a quarter inches by 

 three and a quarter inches, called by 

 photographers a quarter-plate, or by 

 a plate 5X4, according to the ampli- 

 fication you intend to employ or the 

 nature of the object may indicate or, 

 if lantern slides are desired, on a 

 square three and a quarter inches. 

 These ought to have a piece of smooth 

 writing paper gummed on that surface 

 presented to the image; The image 



is then thrown on to one of these, and 

 the hand placed under the focussing- 

 cloth, the carrier is to be moved 

 by means of the screw adjustment till 

 the image of the object is sharply 

 defined on the screen. 



In many writings on this subject it 

 is stated that the actinic and visual 

 focus of microscopical objectives are 

 not coincident. All I can say is that, 

 with a one-third of an inch, which I 

 shall employ this .evening, and with 

 Zeiss's D, no alteration is needed from 

 the visual focus. The screen may now 

 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 experi- 

 ments can determine this. Care 

 must be taken before making the 

 exposure that the light through the 

 objective be cut off till the plate is 

 in position, when it may be allowed 

 to fall on the plate for the requisite 

 time, and then cut off again before 

 removing the plate to the developing 

 dish; this is done, as must be evident 

 to you all, to avoid blurring: the image. 

 I need not say that the only outside 

 light must be a non-actinic red light, 

 and no ray of white light must be al- 

 lowed to reach the plate, or it will be 

 "fogged" — that is, when it is de- 

 veloped it will be veiled by a misty 

 deposit in the film ; therefore no 

 actinic light is admissible till the 

 plate is fixed. 



The developer I use is the ferrous 

 oxalate, made by a saturated solution 

 of protosulphate of iron added to a 

 saturated solution of neutral oxalate 

 of potash in the proportion of one 

 part of the iron to the three parts 

 of the oxalate ; these are best when 

 freshly mixed. If the plate has been 

 rightly exposed the image begins to 

 make its appearance in about forty 

 seconds, and grows under the action 

 of the developer till it is full of detail. 

 When the image shows faintly through 

 the film on looking at the back of the 

 plate I stop- the development, and 

 wash the plate by a good rinsing in 

 rain or distilled water, and then place 



