( 70) 



those 67 and 50 fx be possibly caused by diffraction ; but at all 

 events it is certain that the image of the slit on plate A does agree 

 pretty well in its aspect with the images on those plates of the 

 series for which v > 2, 3, but does not agree with the other images — 

 a peculiarity which is quite compatible with the rather small value 

 of the difference just mentioned. Hence follows, however, as is easy 

 to calculate, that — If we may speak of a wave-leugih of X-rays — 

 we may assume : 



Ax < 0,2 n fi . 



2^. The dark and the bright lines on plate B are less sharply 

 defined ; the dark lines seem even to have passed into rather broad 

 bands with a gradual decay of darkness towards the outer side, the 

 image beginning in this way to resemble, as far as concerns its 

 general character, the former plates of the series of experiments 

 mentioned in Art. 21. It might even be considered, from its general 

 aspect, as being exactly similar to those of the images of the. series, 

 for wliich V is about 1,5. If we might take this similarity for 

 granted, it would follow that 



Ax= ± 0,\8ftft. 



Influence of diffraction in this experiment is also made probable 

 to some extent by the fact that there have been found values for 

 the distance between the dark and the bright fringes in the tran- 

 sition zones, which range between 76 and 91 fi over nearly the 

 whole plate and amount to 78 on an average, so as to point to a 

 distance actually bigger than on plate A; in this respect we should, 

 however, remember that the measurements could not be effected 

 with a high degree of accuracy. On the other hand the point of 

 intersection of the dark fringes on this plate correspond with a lar- 

 ger width of the ditt'raction slit than on plate A, which also seems 

 to point out an influence of diffraction. Nevertheless, though all 

 these particulars may be considered as possibly being caused by 

 diffraction, we ought to be aware it being by no means impossible 

 that they might have been caused by continual, though very slight, 

 vibrations of one or more of the stands, if only the manner in which 

 these stands have been mounted may have not quite prevented them 

 from any such continual motion. 



30. In the neighbourhood of the point-end of the image of the 

 slit on piate A, my attention was repeatedly drawn to something, 

 that in my opinion may possibly be considered as a slight indication 



