A. W. Wright — Cathode Hays and their Effects. 239 



ity, varying with the thickness, gives a corresponding depth of 

 shade in the picture, thus producing an effect of perspective, 

 which in the negative, or a negative transparency projected 

 upon a screen, has a striking effect of relief, and a luminous 

 solidity often of great beauty. 



As in the case of tissues which are rather freely traversed 

 by the rays the differences of shade in the impression are riot 

 very great, the development of the negative requires especial 

 care. It is better to use a developer of less than the ordinary 

 strength, and to use no alkaline accelerator at all, until just at 

 the end of the process, and then very sparingly and chiefly for 

 the purpose of intensifying the picture. This makes the pro- 

 cess very long and tedious, but the results amply compensate 

 for the labor of obtaining them. Aside from this it appears 

 that the photographic plates which have been subjected to the 

 rajs are peculiarly slow, even with the ordinary mode of devel- 

 opment. The picture is a long time in making its appearance 

 and grows very gradually. This is perhaps in part due to the 

 fact that the effect of the cathode rays extends through the 

 entire thickness of the film, which must therefore be thor- 

 oughly developed to the bottom to bring out the full effect, or 

 possibly to a specific action upon the film itself. 



l. ; i;; .feu;. 



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The results of some of the many experiments are shown 

 in the accompanying cut, and in Plate YI. These are selected, 

 not so much for any special interest in the objects themselves, 

 as for the reason that they illustrate some of the charac- 

 teristic features of the pictures obtained by the use of 

 Prof. Eontgen's method. The cut, from a plate made 

 January 30, shows a small paper box filled with cotton 

 in which were imbedded three metallic spheres, which had 

 been used in the laboratory as pendulums. The sphere nearest 

 the edge was aluminium, the one nearest the center platinum, 

 the other brass. They were all of the same size. The cover 

 of the box was in place during the exposure. The box and its 

 cotton filling show little hindrance to the passage of the rays, 

 only the vertical walls showing, with an inward nick where the 



