X-RA V DETECTOR. 



31 



From these facts was evident the need of a scientific instru- 

 ment suitable for studying the phenomena of Rontgen rays, and 

 one that could be perfectly relied upon. An apparatus de- 

 signed for such purposes was constructed by the wTiter in Ma}', 

 1896, under the superv^ision of Professor Rood, of Columbia 

 Universit}', who suggested some of its important devices. Sev- 

 eral forms of the instrument w^ere exhibited before the New York 

 Academy of Sciences at the meeting of November 2, 1896. 



The "X-ray Detector" is shown in outline in figures 8 and 

 9. In these cuts the main casing of the instrument is repre- 



FiG. 8. Side view of the " X-Rav Detector." 



sented by A. It is made of thin wood, that is perfectly im- 

 pervious to ordinary light, and is 30 centimeters in length. The 

 ends of the casing, A, are rectangular, but differ somewhat in 

 dimensions ; at the extreme end, next to B, the outside meas- 



