May 8, 1896.] 



SCIENCE. 



705 



York University on April 22d the corner stone 

 of the first residence hall was laid. The build" 

 ing, which will be ready for use in September, 

 will contain, in addition to rooms for 112 stu- 

 dents, a music room, editorial rooms for the 

 college periodicals, etc. 



Prof. Geoege S. Fulleeton, Vice-Provost 

 of the University of Pennsylvania and Dean of 

 the College, will retire from the latter office 

 and will be succeeded by Prof. "W. A. Lamber- 

 ton, who in turn will be succeeded in the dean- 

 ship of the School of Philosophy by Prof. W. 

 R. Newbold. 



De. Ernest B. Sangeee, of Philadelphia, 

 has been elected professor of pathology and bac- 

 teriology in the Vanderbilt University, Nash- 

 ville, Tenn. 



DISCUSSION AND CORRESPONDENCE. 



ON rood's demonstration of the eegulae 



OE specular reflection of the rontgen . 



RAYS BY A platinum MIRROR. 



On March 27th Prof. Eood published in 

 this Journal a short account of certain experi- 

 ments which he claimed ' i^ointed strongly to 

 the conclusion that in the act of reflection from 

 a metallic surface the Rontgen Rays behaved 

 like ordinary light.' If this sentence means 

 anything, it means that the X-rays underwent 

 regular or specular reflection. On April 10th, 

 however, Dr. M. I. Pupiu published in this Jour- 

 nal an article in which he says, " If I understand 

 Prof. Rood's words correctly, no claim is made 

 by him of a discovery of regular or specular 

 reflection ;" and he then quotes from Rood the 

 sentence given above. The remainder of Dr. 

 Pupin's article is largely devoted to showing 

 that with the methods employed by him no 

 regular or specular reflection could be observed. 

 This last conclusion we are ready to accept. 

 Prof. Rood's experiments, however, were con- 

 ducted in an entirely diflferent manner, as 

 follows : 



Before reaching the sensitive plate the X-rays 

 were obliged to traverse two aluminium plates, 

 each having a thickness of .17mm., and behind 

 them was a drawslide that had proved to be 

 impervious to the sun's light falling on it dur- 

 ing two hours. Over these shields was placed 



a wire netting with openings of ^ inch. The re- 

 flecting surface was a large piece of bright 

 platinum foil, seven inches square. This last 

 was necessarily so arranged that a diffused re- 

 flection from it would have reached all parts of 

 the sensitive plate. In point of fact, however, 

 an image of the wire netting was obtained only 

 on a strip of the plate, viz., on that portion 

 that would be reached by the Rontgen rays in 

 case of their regular or specular reflection. 



The proof that the image of the wire netting 

 on the sensitive plate was really produced by 

 the specular reflection of the X-rays from the 

 platinum was obtained in the following man- 

 ner. The plate which had received the image 

 of the netting made by the X-rays was re- 

 moved from the plateholder and replaced by a 

 fresh plate ; this plate was not screened at all, 

 but its sensitive surface was freely exposed in 

 the dark at night. 



Everything else in the arrangement of the 

 experiment, including the position of the netting 

 in front of the plate, remained as it was during 

 the experiment with the X-rays. One flash 

 from the inductorium was sent into the Crookes 

 tube and the experiment was ended. On de- 

 veloping the plate it was found that the light 

 from the Crookes tube had exactly reproduced 

 in a fi'action of a second what had required ten 

 hours of action of the X-rays. There was the 

 same portion of the plate acted on by the light 

 as had been acted on by the X-rays, and the 

 image of the netting given by the X-rays was 

 reproduced by the light, not generally repro- 

 produced but minutely so ; all the deformations 

 of the image of the netting resulting from the 

 reflection from the uneven surface of the plati- 

 num foil were alike in the photograph obtained 

 by the X-rays and in the photograph obtained 

 by the light. 



I paid repeated visits to Rood's laboratory 

 during the progress of these experiments, and 

 after a careful examination of his negatives no 

 doubt remained in my mind of the fact that he 

 had demonstrated the regular or specular re- 

 flection of the Rontgen rays. 



Prof Rood carried these and other simi- 

 lar negatives to Washington, where he read a 

 paper on the reflection of the X-rays before the 

 National Academy of Science on April 23d. 



