Nipher — Properties of Light-struck Photographic Plates. 163 



The plate holder was held for ten minutes, six inches from a 

 Crookes tube operated by a large induction coil in oil. A 

 perfect picture of the hand could be obtained in six to eight 

 seconds. The same plate was then exposed for two hours to 

 a Crookes tube operated by a large eight-plate influence 

 machine. The plate holder was then put into the camera and 

 exposed to a street scene for ten minutes and was then de- 

 veloped in the light. The result is shown in Fig. 11. For 

 reproduction of form and shadow, this plate could hardly 

 be excelled by a transparency made in the ordinary way. 

 Like the others, it shows no trace of moving objects on the 

 street. 



It has been long known that a slight over-exposure of a 

 plate in the camera sometimes gives a positive picture when 

 developed in the dark room. The experience thus far 

 described made it seem probable that such pictures might also 

 be developed in the light. This was found to be the case. 

 If the proper exposure is one and a half to two seconds, 

 an exposure of a minute is sufficient. Some that have been 

 made have not been very satisfactory. But one has been ob- 

 tained which is even superior to the plate reproduced in Fig. 

 11. It is shown in Fig. 12. For richness of finish and for 

 perfect modulation of light and shadow, this original plate 

 leaves nothing to be desired. During most of the time while 

 being developed, it was held one foot from a sixteen-candle 

 lamp. During some of the time it was held nearer, and 

 during some of the time it was five or six feet from the 

 lamp. 



Figs. 11 and 12 are of course reproductions of the original 

 positives. In these exposures the Cramer isochromatic plate 

 was used. 



In some of these shorter exposures where people or wagons 

 halted on the street, they are shown on the fixed plate. 

 Where they were motionless during the whole exposure they 

 are of course shown with perfect clearness. 



Experiment shows that a conspicuous object two feet 

 in breadth and fifty feet from the camera if moved 

 transversely at the rate of twenty feet per minute, during 

 an exposure of one minute, will show on the plate as 



