170 THE AMERICAN MONTHLY [August, 



as getting a good plate and mastering its peculiarities are concerned, for, 

 however well the working of any one plate may be understood, results 

 cannot be obtained from it alone, upon all kinds of objects, equal to 

 those obtainable when different makes of plates are intelligently used, 

 in a manner to make their peculiarities bring out, in the resulting nega- 

 tive, the effect sought for. For instance, if the object to be photographed 

 has but little contrast, and a plate giving great contrast and a short range 

 of half tones be used, a good printing negative will usually be obtained, 

 while, if a plate having opposite qualities were used, no amount of care- 

 ful exposure or development would give a negative having sufficient 

 contrast to print properly. Similarly, with an object having great con- 

 trasts, a plate giving little contrast and long range of tones, will give a 

 negative in which the contrasts of the object are so lessened that print- 

 able details are given in the densest parts, while, were a plate having 

 opposite qualities used, the strong contrasts of the object would be so 

 reproduced, or exaggerated that a print devoid of all detail could be ob- 

 tained only. As in photo-micrography, owing to the peculiar nature 

 of the objects to be photographed, great difficulties are often encount- 

 ered, the ingenuity of the operator often being taxed to the utmost, it 

 follows that a proper selection of the plate to be used will add greatly 

 to his resources, and will enable him to obtain results which could not 

 be obtained were only one make of plates used, whatever legerdemain 

 of exposure or development he might practice. 



But, in order to take advantage of the different properties of different 

 plates, it is necessary to know exactly how they differ ; and this must 

 be determined not by exposing the plates to be compared in a camera 

 where the light may be constantly varying, and where the personal 

 equation of the operator may enter as a disturbing factor, biit in a man- 

 ner by which each shall receive equal treatment. For purposes of com- 

 parison, I have used a pad of thin white tissue paper (onion skin), 4X 

 4^ inches in size, made of superimposed pieces of the paper, each piece 

 being 4 inches long and \ inch narrower than the next sheet underneath. 

 This pad, when placed on a piece of clear glass in a 4 x 5 printing 

 frame and viewed by transmitted light, gives nine gradations of density 

 from clear glass up. Such a pad answers for all practical purposes, 

 though one ^\ inches long placed in a 5 x 8 printing fi'ame and used 

 with strips cut lengthways from 5x8 plates, will give a longer range 

 of gradations. To test two or more plates, a strip about one inch wide 

 and five inches long is cut from each, and placed side by side, film side 

 down, on the pad in a 4 x 5 printing frame. They are then clamped 

 in the frame, exposed for one instant to diffiise day light, or for a few 

 seconds to lamp light ; and are then all developed together in the same 

 developer. It is best to develop for fully twenty minutes in a covered 

 tray, with a developer containing a rather large quantit}' of sodium 

 sulphite. If about 30 grains of the granular sulphite is used to each 

 ounce of developer, yellowing of the films, which might be produced by 

 the prolonged development, will be prevented ; and this without any 

 ill-effect on the resulting negatives. Development for fully twenty 

 minutes is recommended in order that development be fully completed, 

 i. e., that all the molecules of silver acted upon by light be reduced, for 

 in this way only can the exact properties of all the strips be brought out, 

 inasmuch as some plates develop more rapidly than others, and a stop. 



