244 W. L. Robb— Solarization Effects in 



necticut, and by the General Electric Co. at their lamp works 

 at Harrison, N. J. In the absence of any exact method of 

 expressing for any given set of apparatus its power of produc- 

 ing Rontgen rays, the statement that the photograph of a por- 

 tion of a hand reproduced in Plate VIII, fig. 1, was taken with 

 the apparatus just described, will serve to show its character. 

 The time of exposure was 5 seconds and the distance of the 

 hand from the anode 25 cm . 



Solarization effects were first noticed by the author in connec- 

 tion with the halos surrounding the Rontgen ray photographs 

 of pieces of metal. These halos were in general similar to 

 that shown in Plate VIII, fig. 2, which is a reproduction of 

 the photograph of an aluminum cube, the edge of which was 

 2*5 cm . Surrounding the portion of the photographic plate 

 directly under the cube is a band in which the plate was some- 

 what affected by the rays. Just outside of this first band is a 

 second one, in which the effect upon the photographic plate 

 was greater than upon any other part of the plate. This halo 

 is easily explained when we consider that in a single focus tube 

 the Rontgen rays come from a considerable area of the anode 

 and that consequently the shadow of the object is surrounded 

 by a penumbra in which the intensity of the radiation increases 

 from the object outward. If the exposure is sufficient to pro- 

 duce solarization, we should have a band in the penumbra 

 where the effect upon the photographic plate would be a 

 maximum exceeding even the effect upon the part of the plate 

 entirely beyond the shadow. The photograph reproduced in 

 Plate VIII, fig. 2, was taken with fifteen minutes' exposure at 

 a distance of 15 cm . 



The experiment was repeated with cubes of iron, copper, 

 paraffin, and glass, all of which gave similar halos. In general, 

 the image on the photographic plate was visible to the eye 

 before being placed in the developer — a phenomenon that 

 accompanies solarization when produced by ordinary light. 



The following experiments were made in order to prove the 

 correctness of the above explanation and to demonstrate the 

 possibility of a photographic plate becoming solarized by the 

 Rontgen rays. 



Portions of several plates were covered with pieces of com- 

 mercial tinfoil and then exposed in succession for different 

 times to the action of the Rontgen rays. It was found that with 

 short exposures a negative was obtained, and with long expo- 

 sures the image was reversed ; the long exposed plates giving a 

 positive when developed. Plate IX, figs. 1 and 2, and Plate X, 

 fig. 1, are reproductions of photographs obtained when a por- 

 tion of the photographic plate was covered with one layer of 

 commercial tinfoil about 5 cm square and 0"0015 cm thick, and 



