Intelligence and Miscellaneous Articles, 463 



silver bromide. Combined in dilute potassium-bromide solutions 

 with a standard electrode, the electrode in question showed 

 sensitiveness to light. This is easily proved with the help o£ 

 a quadrant electrometer (Luggin, Ostwald's Zeitschrift fur phys. 

 Chemie, xiv. p. 387, 1894). A candle placed at a distance of 25 

 cm. from the electrode produced in half an hour a diminution of 

 0-022 V. in the electromotive force of the combination 



Zn/Zn S0 4 aq+K 2 S0 4 aq + BrK aq+Br Ag/Pt. 



At the same time it is to be remembered that the light only struck 

 one side of the platinum-foil, while the other, which was also 

 sensitized, remained dark. If now a carefully enclosed discharge- 

 tube through which ind action-sparks passed was substituted for 

 the candle, a diminution in the electromotive force could also be 

 observed. With a small induction-coil the change amounted to 

 0*017 volt in the coarse of 45 minutes, and in another experi- 

 ment with a larger induction-coil to 0*019 in 40 minutes. 



By a corresponding increase in the delicacy of the method, the 

 electrochemical deportment of Bontgen rays may possibly furnish 

 a more convenient method of investigating them than that with 

 the help of photography. — Wiener Berichte Feb. 6, 1896. 



TRIANGULATION BY MEANS OF THE CATHODE PHOTOGRAPHY. 

 BY JOHN TROWBRIDGE. 



Photography by means of the Bontgen rays seems already to be 

 of great importance in examining certain portions of the human 

 body to determine the presence of metallic bodies, calcareous 

 formations, and fragments of glass. The shadow pictures as they 

 are taken at present, however, do not give the approximate 

 position of the shots, for instance, embedded in the flesh. They 

 indicate only the line in which they are situated. It occurred to 

 me that the principles of triangulation could be applied with 

 success to determine more exactly the position of the metallic 

 particles. I was led to this conclusion by considering Bumford's 

 photometer. This instrument, it is well known, consists merely 

 of a vertical rod placed opposite a suitable screen of white paper. 

 The two lights, the intensities of which are to be compared, are 

 placed in a fixed position, and throw two shadows of the rod on 

 the screen. From a measurement of the positions of the lights 

 when shadows of equal intensity are thrown on the screen, an 

 extinction of the brightness of the lights can be obtained. More- 

 over, by measuring the distance between the shadows, and by 

 drawing lines from them to the lights, the position of the rod 

 throwing the shadows can be determined. This position is 

 evidently at the intersection of these lines. 



I have used two Crookes' tubes with two terminals making an 

 angle with each other, and have employed a to-and-fro excitation 

 by means of a Tesla coil. A suitable screen of glass shielded the 

 sensitive plate first from one cathode and then from the other. 

 From the distance between the shadow pictures of a shot, for 

 instance, on the back of the hand and from the position of the 



