Apeil 10, 1896.] 



SCIENCE. 



541 



with certainty. A refiection from metallic 

 surfaces in the immediate vicinity of a pho- 

 tographic film was detected, " but," quoting 

 Eontgen's own words, "if we connect these 

 facts with the observation that powders are 

 quite as transparent as solid bodies and 

 that, moreover, bodies with rough surfaces 

 are in regard to the transmission of X-rays, 

 as well as in the experiment just described, 

 the same as polished bodies, one comes to 

 the conclusion that regular reflection, as 

 already stated, does not exist, but that the 

 bodies behave to the X-rays as muddy 

 media do to light." 



In face of these observations made by 

 Prof. Rontgen, Prof. Eood's and Mr. Tesla's 

 experiments must be interpreted as a confir- 

 mation of Prof. Eontgen's results, and not 

 as a demonstration of the existence of a 

 regular refiection. If I understand Prof. 

 Rood's words correctly, no claim is made 

 by him of a discoveiy of regular reflection; 

 for he says: " These facts and the character 

 of the deformations point very strongly to 

 the conclusion that in the act of reflection 

 from metallic surface the Rontgen rays be- 

 have like ordinary light." Mr. Tesla, how- 

 ever, infers with much confidence regular 

 reflection from his theory of bombardment. 

 His experimental method is the same as that 

 of Prof. Rood ; that is, he places a reflecting 

 plate at an angle of forty- five degrees to the 

 direct ray and then places the photographic 

 plate at right angles to the direction in 

 which the reflected ray should pass if reg- 

 ular reflection existed. On account of the 

 greater power of his apparatus, his time of 

 exposure was one hour, whereas that of 

 Prof. Rood was ten hours. It is evident, 

 however, that an eftect upon the photo- 

 graphic plate does not prove the existence 

 of regular reflection, as Mr. Tesla maintains 

 with much assurance and with much re- 

 joicing over the realization of the prophesy 

 which he made, inspired by his molecular 

 bombardment theory. 



In my experiments on reflection I aimed 

 at getting rid of the photographic plate and 

 substituting the fluorescent screen in its 

 place. Two conditions had to be fulfilled 

 to make this substitution possible. First, 

 a' very powerful and perfectly steadj^ dis- 

 charge had to be maintained. Secondly, a 

 verj^ sensitive fluoroscope had. to be em- 

 ployed. The first was accomplished by the 

 apparatus and the operations described 

 above. The second was found in Mr. 

 Edison's tungstate of calcium fluoroscope. 

 The tube was placed between two thick 

 planks of pine coated with sheet lead J^ of 

 an inch thick. This screening was found 

 to be somewhat insufBcient when the tube 

 oj)erated at maximum efficiency and an- 

 other screen consisting of a thick copper 

 plate had to be employed. The planks 

 were placed so as to form a wedge around 

 the tube. The cathode streamer was hori- 

 zontal and passed through a vertical slit 

 formed by the edges of the two screening 

 lead-covered planks. In front of this slit 

 was a fixed pivot on which a mirror could 

 be rotated. The mirror consisted of a pol- 

 ished sheet of platinum pasted upon a rec- 

 tangular piece of pine board of nearly the 

 same area as the platinum sheet and about 

 one inch thick. The slit was made yig- in. 

 wide and its image examined was by means 

 of the fluoroscope. The tube was six inches 

 from the slit. 



a. Quite near the slit the image was sharp 

 and intense. But as the fluoroscope was 

 gradually moved away from the slit its 

 image broadened out somewhat, and there 

 was at each side of it a diffuse border. At 

 about two inches from the slit the image of 

 the slit looked like a wide spectral line upon 

 the less luminous background of a wide 

 band which shaded oflT gradually into the 

 dark space of the screen. With increase of 

 distance the relative intensities of the two 

 grew more and more equal, and at about six 

 inches from the slit the whole fluorescent 



