162 Trans. Acad. Sci. of St. Louis. 



Fig. 1. In order that the X-ray picture of the metal fittings 

 of the camera, and the light picture of the object in front 

 of the lens may be superposed on the fixed plate, the 

 diaphragm of the camera must be so set that the two pictures 

 will develop in the same time with the same developing 

 bath. 



The results already described suggested that in ordinary 

 photography the exposure might be so modified that the 

 picture might be developed in the light. 



In the first attempts that were made the object was a street 

 scene. The exposures were from one to three and a fourth 

 hours. The pictures developed in the light with perfect 

 clearness. They are of course positives. They appear some- 

 what unpromising at first, Avhile in the developing bath, and 

 one is tempted to abandon them as failures, as indeed some 

 of them may be, until experience is gained. The pictures 

 obtained by these long exposures show some very interesting 

 features. They show no trace of moving objects on the 

 streets. In some cases hundreds of people passed. In one 

 case ten street cars were blocked for twelve minutes, in the 

 foreground, and cars were passing at the rate of 70 to the 

 hour. Wagons were driven to the curb to deliver goods to 

 houses, and people were standing on the street corners wait- 

 ing for cars. In an exposure of an hour no trace of these 

 objects could be seen on the plate when developed. The 

 street appeared absolutely deserted. The car tracks show 

 with distinctness. In one exposure of three hours and forty- 

 five minutes a team and wagon stood in one position for 

 twenty- eight minutes, and no trace of them appeared. If the 

 exposure of the same plate is only for one second, these mov- 

 ing objects are all shown. Another feature of these long 

 exposures is the entire absence of shadows. It is somewhat 

 difficult to account for this, as it hardly seems possible that 

 their motion is sufficient^ 7 rapid to produce this result. The 

 sky appears absolutely uniform. Clouds which were in 

 marked contrast in one case yield no trace upon the picture. 

 An attempt was then made to shorten the time of exposure 

 and still permit development in the light. This was done by 

 subjecting the plate, while in the plate holder, to the X-ray. 



