90 . THE AMERICAN MONTHLY [April, 



the flame serves to concentrate the light on the object. A curtain of 

 bhick velvet falls over the front of this arrangement, shutting all light 

 in, and a shutter cuts oft' the rays coming through the objective till all 

 is ready for the rays to fall on the sensitive plate during the proper 

 time of exposure. 



The lamp lighted and placed inside of .the box is allowed to burn a 

 short time before commencing work, so that the wood and brass work 

 may be warmed. If this is not done the expansion of these materials 

 after focusing the object will result in a blurred picture. A microscopi- 

 cal slide may next be placed in position, and its projected image ar- 

 ranged on the white paper surface of the focusing screen. Leiirn by 

 the chai-acter of this image whether it will require a long or a short ex- 

 posure, whether it reveals much detail or is marked by its entire ab- 

 sence, or whether its color favors photography or not. If the objector 

 its image possesses detail of a fairly well marked character, and the ob- 

 ject is not too thick, a successfvd result will follow the correct exposure. 

 And now you are brought face to face with the first of the difficulties. 



In the manner of normal exposures by lamplight, Mr. W. H. Walms- 

 ley gives the following table, which may be taken as approximate, but 

 may require modification for each operator: When using a i^-in. ob- 

 jective, 3-45 seconds; f-in. objective, 7-90 seconds; i\-in. objective, 

 ^-3 minutes; ^-in. objective, 2-7 minutes; yV-i". objective, 4-10 min- 

 utes. 



Having selected an object and focused the image, cut oft^the rays of 

 light from the screen and shut in every vestige of light. Now, being 

 in perfect darkness, light the non-actinic lamp ; these are sold of various 

 patterns, but may not be actinically safe. That recommended is a 

 paraffine lamp with all light blocked out through the reservoir, an ar- 

 gand wick, and a tubular chimney well coated inside and out with 

 Thomas' ruby varnish. This will afford abundance of safe light at 

 eighteen inches distance. By this light take the sensitive plate from its 

 box and put it into the focusing frame, when its gelatine surface ought 

 to be in exact register with the fine diamond markings by which you 

 get the time focus. Then open your objective, and let the image of 

 your preparation fall on the gelatine plate for the number of seconds 

 or minutes given in Mr. Walmsley's table, after which shut oft' the 

 light again, and proceed to develop. Some operators prefer the ferrous 

 oxalate developer, while others adopt that which is known as the alka- 

 line pyrogallic acid. Some who have used both, although having got 

 very good negatives with the pyrogallic acid, prefer the ferrous oxa- 

 late, because it does not stain the fingers. As some may like the sim- 

 plicity as well as the cleanliness of this developer, it may be well to 

 give the formula fo'r making it. Having made two saturated solutions, 

 one of neutral oxalate of potash and another of sulphate of iron, add 

 them together in the pi'oportion of one part of iron to three parts of 

 oxalate of potash, taki7ig care always to add the iron to the potash. 

 It makes a dark sherry-colored mixture. If it is feared that the plate 

 has been slightly over-exposed, add a few drops of a ten per cent, so- 

 lution of bromide of potassium, which, acting as a restrainer, keeps 

 back the too rapid development of the image. Keep up the develop- 

 ment until the general ground of the plate does not transmit any light, 

 and every detail will be brought out in the image. Then give the plate 



