THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XXI. — On the regular or speGular reflection of the 

 Bontgen Rays froTn polished metallic surfaces ; by Prof. 

 O. N. Rood of Columbia University. 



The source of the electricity in all the experiments detailed 

 below was an ordinary induction coil made by Ruhmkorff : its 

 length was 30 centimeters, its diameter 13"5. When the coil 

 was in action a current of 4*8 amperes traversed it, and fur- 

 nished a spark 90™°^ in length. In none of the experiments 

 described in this paper did the discharge tubes heat sensibly. 

 The tube employed in the earlier experiments had a diameter 

 of 47™°", and contained a small calcined shell, which when 

 acted on by the cathode rays, furnished X-rays quite abundantly 

 from an area about 4°"™ square, and in smaller amounts from 

 other portions of the shell and from the walls of the tube, as 

 was proved by the aid of pin-hole photographs. 



1. Experiment with platinum foil, unmou^ited. 



The first decided indication of regular or specular reflection 

 of the X-rays was obtained on March 13th, after an exposure 

 of ten hours, a sheet of platinum foil 17*8 centimeters square 

 being employed as the reflecting surface ; the total distance 

 from the walls of the vertical discharge tube to the plate- 

 holder was 165™°". A short account of the result obtained was 

 published in Science, on March 27th, 1896. 



In this experiment the sensitive plate was shielded by a 

 draw-slide that proved impervious to bright sunlight during an 

 exposure of seven hours : in addition to this protection from 

 ordinary light, it was completely covered by a plate of 

 aluminium having a thickness of 0'17"°'j and the central por- 



Am. Jour. Sci.— Fourth Series, Yol. II, No. 9. — September, 1896. 

 13 



