174 0. N. Rood — Reflection of the Rontgen Rays. 



tion of this plate was again covered bj a horizontal strip of 

 the same material, 25°""" broad. Over this a netting of iron 

 wire was fastened, the distance of the wires apart being ^'1^^^ 

 their thickness 0'54°^°'. This netting was destined to furnish 

 the image or shadow-picture. I may remark in passing, that 

 nettings like this, or coarser, are very useful in experiments on 

 the X-rays, as they furnish accurate information as to uni- 

 formity of illumination, single or double sources of the rays, 

 and also with regard to the relative transparency of objects 

 placed on or in front of the plate-holder. It is hardly neces- 

 sary to add that in the experiment with the platinum foil the 

 plate-holder was protected by sheet lead from all direct emana- 

 tions of the discharge tube. The angle of incidence was made 

 as near 45° as could be accomplished with a divergent beam. 



After the impression due to the reflected X-rays had been 

 obtained, the sensitive plate was removed from the holder, 

 also the shields of aluminium and the draw-slide, the wire net- 

 ting alone being allowed to remain. The plate-holder, being 

 then provided with a fresh sensitive plate, was replaced exactly 

 in its original position, and exposed in the dark to a single dis- 

 charge of the tube, the ordinary light of which was reflected 

 to the naked plate by the foil. The image on the comparison 

 plate thus obtained was of course due entirely to ordinary 

 light that had been regularly reflected from the platinum, and 

 the deformations of this image served to answer the question 

 as to whether the X-rays also had undergone regular or specu- 

 lar reflection or only diffused reflection, or a mixture of both. 



mm 



The accompanying woodcuts, figures 1 and 2, will serve to 

 give some idea of the images obtained in the two cases. It 

 will be noticed in figure 2, the picture obtained by ordi- 



