LATEST DEVELOPMENTS WITH THE X RAYS. 667 



submitted to the rays. This sheet should be connected to the 

 earth. This fact should be borne in mind when we come to speak 

 of the electrical region outside a Crooke's tube. 



Many investigators, reflecting upon the singular fact that the 

 rays pass so freely through thin aluminum and that, on the con- 

 trary, glass absorbs such a large percentage, concluded that Crooke's 

 tubes provided with aluminum windows would be an improvement 

 upon the thin incandescent lamplike bulbs now used. The glass 

 of these bulbs is very thin, not more than one thousandth of an 

 inch in thickness, where the rays emerge, not thicker than a sheet 

 of ordinary note paper, and the absorption of such a sheet of glass 

 is so small that it can not be detected by photography. Thus a 

 sliver of glass of this thickness in the hand would not appear on 

 the X-r.'ay photograph of this member, and would not cast a shadow 

 in the fluoroscope. There does not seem, therefore, any advantage 

 in supplying a Crooke's tube with an aluminum window. The 

 mechanical difficulties, too, in accomplishing this are very great. 

 There is no way of joining the thin aluminum disk to the glass so 

 that an air-tight joint can be made. In the process of exhausting 

 the Crooke's tube, the tube must be heated to a comparativel}' high 

 temperature in order to drive off the air which clings to the inside 

 of the glass. The rise of temperature would soften or melt any 

 current which might be used to mftke the aluminum adhere to 

 the glass. 



We can not expect, therefore, any improvement in the direc- 

 tion of aluminum windows. At one time, I suppose that the rays 

 were highly absorbed in passing through atmospheric air, and that 

 it would be an improvement in the application of the rays to sur- 

 gery to interpose, so to speak, a vacuum chamber between the body 

 and the source of the X rays. The experiment led to some inter- 

 esting results, but not in the direction anticipated. 



The vacuum chamber consisted of a glass cylinder three feet 

 long and about eight inches in diameter. The two ends were 

 closed by sheets of aluminum, and it could be exhausted through 

 a side tube. The reader will immediately ask, in view of what 

 has been said. How could the glass tube be hermetically closed 

 with sheets of aluminum? This was indeed a difiicult matter, but 

 less difiicult than in the case of the Crooke's tube, for the ends of 

 the glass cylinder were provided with heavy brass flanges, which 

 were perfectly flat, and the sheets of aluminum lying smoothly 

 could be confined by many bolts betAveen the fiange and suitable 

 brass heads. This cylinder, having been exhausted, was placed 

 between the Crooke's tube and the 'arm, for instance, in the hope 

 that a greater depth of human flesh and tissue might be penetrated 



