212 Trans. Acad. Sci. of St. Louis. 



which will serve as a background. Any other dark back- 

 ground will of course answer the purpose. After 

 snapping open the shutter, walk to a point about 100 feet 

 distant, the camera having been focused for that dis- 

 tance, and stand motionless for two or three minutes. Then 

 step sidewise four or five feet and stand for an equal time . 

 Then walk back and close the shutter. The two figures will 

 seem practically alike if the sunlight has not changed, and 

 the darker background will not appreciably show through them. 

 The plate will show no trace of the motions, and the figures 

 will be as clear and distinct as in a good negative. 



Of course the same thing can be done in the ordinary 

 negative process by so arranging the conditions that the time 

 of exposure is sufficiently lengthened. 



In order to make the positive photography as useful as 

 possible, it is necessary to find a developer which will bring 

 out a clear positive with as small an exposure as possible. It 

 seems certain that it must differ from any developer used in 

 ordinary photography. The method of restraining an over- 

 exposed negative is known, in order that it may be developed 

 as a negative. If we consider this plate as an under-exposed 

 positive, how shall it be pushed along over the zero condi- 

 tion, and developed as a positive? That answer may be given 

 in part. It must be developed in the light. A poor negative 

 may be developed in a lighted room, and a poor positive may 

 be developed in a dark room. These are not the conditions 

 which yield the best results. 



The writer had great expectations of the developer used by 

 Waterhouse for producing positives in the dark room with 

 ordinary exposures. The formula for this developer, as 

 given in various works on photography is : — 



Parts. 



A. Eikonogen 5 



Sulphite of soda 10 



Water 100 



B. Carbonate of soda 4 



Water 100 



C. Phenyl-theocarbamide 1 



Water ; 2000 



For developing take of A 1 , of B 2, of C 1 and of a 10 per 



