Nipher — Relation of Direct to Reversed Photographic Pictures. 59 



is still negative is a small area in the dense foliage in shadow, 

 on the right of the picture. 



Fig. 13. Exposure E = 1,440,000. 1=0. 



This picture is completely reversed. 



Fig. 14. This plate had the same exposure as the last, but 

 was developed in daylight where /= 200. 



Fig. 15. Exposure 5,000,000. 1 = 200. 



The details in the dense shadows are admirably shown in 

 this picture. The exposure was seven hours to diffuse day- 

 light in front of an inclined skylight about ten feet square. 

 The exposure was to a northern sky. 



Fig. 16. This exposure was made like the last one, but 

 lasted for sixteen hours on two days. The plate was devel- 

 oped in the same light, with a mirror reflecting light upward 

 upon the under side of the plate. The traces of two ribs in 

 the bottom of the glass tray, are shown on the plate. 



Fig. 17. This picture is from the negative shown in Fig. 2, 

 Plate 2. It is a reproduction of a print from that negative, 

 which was made by ordinary methods. It is to be compared 

 with Fig. 18, made from the same original as Fig. 16, which 

 is from an exposure 11,500,000 times as great. 



A number of good pictures have been developed in direct 

 sunlight, but they have been lost or destroyed, and it has since 

 been found difficult to produce as good ones as were formerly 

 made. There is strong evidence that there is a discontinuity 

 in the conditions of sunlight development like that shown by 

 the zero line at the critical illumination. One difficulty in the 

 study of this subject, is the extreme variability of sunlight. 

 The actinic value of sunlight is also enormous compared with 

 the standard illumination used in this work. An exposure of 

 about a quarter of a second is greater than an exposure of 

 120,000 seconds at a distance of one meter from a 16-candle 

 lamp. The developing of good pictures in direct sunlight is 

 therefore in an uncertain condition as yet, and is receiving 

 further study. 



If the plan of laying the developed plates down upon a 

 table at points determined by J3 and /, had proved practi- 

 cable, it would have been possible to draw on the diagram, 

 lines passing through points where the plates have equal ex- 



