March 27, 1896.] 



SCIENCE. 



465 



est care was taken to obtain the most sen- 

 sitive plates and the most powerful devel- 

 oper known, and that this matter gave 

 much more trouble than the experiment 

 just described. Ogden IST. Eood. 



Columbia Univkesity, New York. 



FURTHER EXPERIMENTS WITH X-RAYS. 



Photographs have now been obtained 

 with several of the Crookes tubes in the 

 cabinet of the Dartmouth Laboratory, but 

 the one referred to in a previous communi- 

 cation is by far the most efficient, and it 

 has been used in nearly all the experiments 

 now to be described. This tube was made 

 by Stoehrer, of Leipzig, being No. 1147 of 

 his catalogue, where it is designated as 

 Puluj's neue Phosphorescenz-Lampe. It 

 contains a mica diaphragm coated with 

 some phosphorescent substance, and gives 

 quite a brilliant green light when in action 

 (although this brilliancy is doubtless im- 

 material to the production of the X-rays). 

 As to the source of the X-rays developed 

 by this tube it may be stated that a vari- 

 ety of experiments have shown that they 

 originate in the diaphragm itself where ex- 

 posed to the cathode rays, and not to any 

 appreciable degree ia the glass around the 

 diaphragm. Cathode rays which pass 

 through the diaphragm appear, however, 

 to develop X-rays at the surface of the glass 

 where they impinge. 



The method first adopted for determin- 

 ing the position of the source was that of 

 calculating its distance from the plate from 

 the magnification of the shadows of inter- 

 vening opaque objects, but this procedure 

 brought out anomalies, as will presently be 

 mentioned. By bringing the plate near the 

 tube, the diaphragm could be made to cast 

 its own shadow, and the resultrag appear- 

 ance leaves no doubt that the X-rays chiefly 

 originate in a limited portion of the dia- 

 phragm. The method of using a series of 

 parallel films leads to the same conclusion. 



and indicates that in this tube the rays do 

 not proceed directly from the cathode itself. 

 Lenard has observed that the cathode 

 rays are diffracted around the edges of ob- 

 stacles. In case of the X-rays our experi- 

 ments indicate an effect apparently some- 

 what the reverse of this. While the shadow 

 of an obstacle is always magnified, and often 

 to a degree disproportionate to the distances 

 involved, we have obtained several plates 

 showing the impression from an aperture 

 in an opaque object to be slightly minified, 

 when the plate is sufficiently near the object. 

 This would point to an outward rather than 

 an inward bending of the rays. In this 

 connection attention is called to a curious 

 phenomenon presenting to the eye the ap- 

 pearance of irradiation, although it is diffi- 

 cult to believe that any real analogy to 

 irradiation is offered. 



Fig. 1. DisTOETiosr of Coins Photographed 

 WITH X-Eays. 



The coins shown in Fig. 1, are a silver 

 dollar, a dime, and two nickels, in con- 

 tact, all perfectly round ; a glass rod (end- 

 ing in a brass cap) touches the dollar, 

 and a small piece of hard rubber prevents 

 it from rolling. The line across the plate, 

 through the shadow of the dollar, is the 

 image of the mica diaphragm, the plane of 

 which was nearly perpendicular to the 



