( 422 ) 



a : width of the first slit in iiiicrons. 



s : ,, „ „ diffraction slit „ „ 



a : distance between first and diffraction slit in cm. 



b : „ ^ diffraction slit and photografic plate in cm. 



a = 75 cm. « : 2 a 14 jM. 



Time 



of exposition 



Hours. 



NO. of 

 experiment. 



25 

 •25 

 U 

 14 

 25 

 18 

 18 

 18 



1 

 20 

 45 

 75 

 75 

 105,5 

 1 

 75 

 75 



29 



57 



60 



60 



100 



150 



30 



130 



200 



In the experiment N''. 1 a plate sensitive on both sides was used — 

 mark B II of the Actiën- Gesellschaft fur Anilin-Fabrikation. The 

 image on the second side of the plate however was many times 

 fainter than that on the first side; moreover on account of the 

 rather strong fog it seemed very desirable to destroy the image on 

 the second side and to remove the gelatine film; in the other expe- 

 riments LOMBERG-plates were used. The plates were developed a 

 very long time (at least half an hour) using rodinal (1 at 35), po- 

 tassium bromide being added. 



In experiments 5 and 8, the photographic plate was pressed against 

 the brass plate, on which the diffraction slit was mounted. Measu- 

 rements, in order to give the width of the slit, were made on the 

 images obtained by these experiments, greater accuracy being attainable 

 in this manner than by direct measurement of the slit; on account 

 of the small distance between the plate and the slit, the image could 

 not be sensibly broadened nor by diffraction nor by the X slit being 



