464 



SCIENCE. 



[N. S. Vol. III. No. 65. 



set of experiments, and indications were 

 almost immediately obtained that a small 

 percentage of the so-called X-rays were re- 

 flected by a platinum surface placed at 

 an angle of forty-five degrees. The expos- 

 ure of the sensitive plate, however, was 

 not sufficiently prolonged ; neither was it 

 properly shielded from the anode end of the 

 discharge tube. Matters were finally ar- 

 ranged so that the plate-holder was com- 

 pletely shielded from all parts the dis- 

 charge tube by screens of heavy sheet lead, 

 and on March 13th, after an exposure of 

 ten hours, a satisfactory negative was ob- 

 tained, capable of furnishing prints. 



The apparatus employed was of the sim- 

 plest character; a coil of moderate size, made 

 by Ruhmkorff more than thirty years ago, 

 was excited by a current suitable for class- 

 room experiments, no condenser whatever 

 being employed. The Crookes' tube was of 

 German make, and had originally been in- 

 tended only for class demonstrations. With 

 aid of a fluorescent screen it had been care- 

 fully studied, and the best portion of it was 

 employed. The reflecting surface consisted 

 of a new sheet of ordinary platinum foil, 

 which was held rather loosely against a 

 plate of glass, no attempt being made to re- 

 move its accidental deformations, which 

 were mainly paralleled to the axis of the 

 cylinder, which it had formed when rolled 

 on its stick. These elongated deformations, 

 convex and concave, were placed vertically. 



The plate holder, in addition to its 

 draw slide, was completely covered by a 

 plate of aluminium with a thickness of 

 0.17 mm.; the central horizontal portion of 

 this was again covered by a broad strip of 

 the same aluminium plate, and over the 

 whole was fastened a netting of iron wire, 

 destined to furnish the image. I may re- 

 mark in passing that I have found wire 

 netting very useful in other experiments 

 with the X-rays, as it gives instant informa- 

 tion as to the condition of the field with 



regard to uniformity of illumination, single 

 or double sources of the rays, and also with 

 regard to the relative transparency of ob- 

 jects placed on the plate holder. 



The plate holder being arranged as indi- 

 cated, care was taken that rectilinear 

 emanations from the discharge tube should 

 not even reach the external wooden por- 

 tions of its frame. 



After an exposure of ten hours it was 

 found that a good image of the netting had 

 been produced on the vertical strip of the 

 plate exposed to the reflected rays. This 

 image had various deformations, the verti- 

 cal lines representing the netting being as a 

 general thing most distinct ; in some places, 

 however, the horizontal lines had the upper 

 hand, and there were a few spots where 

 both were equally distinct. The image un- 

 der those portions protected by two thick- 

 nesses of aluminium plate was perhaps a 

 trifle fainter than that on the rest of the 

 plate. These facts and the character of the 

 deformations point very strongly to the 

 conclusion that in the act of reflection from 

 a metallic surface the Rontgen rays behave 

 like ordinary light. 



Photographic experiments were then 

 made to ascertain the percentage of the 

 rays reflected. A plate from the same box 

 was placed at a corresponding distance (6.5 

 inches) from the discharge tube, and the ex- 

 posure diminished, till a similar image was 

 obtained. It was, of course, protected in the 

 same way as in the experiment on reflection, 

 and developed for the same length of time. 

 This image was not in any way deformed. 

 After an examination of it by Mr. F. J. 

 Harrison, Professor Hallock and myself, 

 the conclusion was reached that the re- 

 flected image had the same intensity. This 

 would indicate that platinum foil reflects 

 the y^ part of the X-raj'S incident on it 

 at an angle of 45°. Of course this flgure 

 is to be regarded as a flrst approximation. 



In conclusion, I may add that the great- 



