( 424 ) 



cannot explain the broaden! ngs of the image, which as we observed 

 occur with the narrowing of the diffraction slit. 



Tt might however be argued that if the influence of the width of 

 the first slit is taken into account, also with linear propagation of 

 the rays, the image of the slit tnight make upon us the impression 

 of a broadening with the gradually narrowing of the second slit. 

 In this case however the apparent limits of the image should cit 

 the idmost diverge at the same rate as the edges of the second 

 slit approach each other. In our experiments however the diffrac- 

 tion slit narrows in so slow a manner that a broadening from this 

 cause would be totally imperceptible. 



Hence we can only draw the conclusion, that the broadenings 

 of the slit image we have observed must be attributed to a Diffrac- 

 tion of the Röntgen rays. With this hypothesis the different 

 broadenings of the slit image, which are to be interpreted as mani- 

 fold formations of plumes, are easily explained, because it is only 

 necessary to suppose that there are rays of considerably different 

 wavelengths, rays of some definite wavelengths possessing greater 

 energy than others; the rays with great energy cause the separate 

 broadenings resembling plumes, the height of the ray source favou- 

 ring haziness. 



The small intensity of the broadenings resembling plumes, the 

 haziness of their edges make accurate measurements and hence a 

 precise determination of the wavelength impossible. We were obli- 

 ged to make only an estimation of the wavelength of the more 

 prominent rays. 



In Fresnel's diffraction theory is introduced the quantity v ; in 

 conformity therewith we now introduce the quantity r^, as given 

 by the relation 



v, = s\/ 



2(a-\-b) 



ibX 



This quantity determines, s, a, h and I being given, the kind of 

 the primary diffraction image to be expected, so that by means of 

 CoRNu's spiral the intensity curve of the diffraction image can be 

 constructed. We have done so for the values 2, 1.5 and 1 of the 

 quantity Vs- The width of the first slit, f>, must however be taken 

 into account, or which comes to the same thing, from the primuy 

 the secondary diffraction images must be deduced. ') 



') C. H. Wind, //Over deu invloed van de afmetingen der liehtbrün bij FBESNF.L'sche 

 buigingsverscbijnseleu". Verslag der vergad. April 1897. 



