XIX, 1. Kheinberg: Common Basis ofthe Theories ofMicroscopic Vision. 17 



in divisions, we can reatlily observe how tlie expaiisiou of P' and 

 tbe distance from the ceutre of P' to *S' doubles as we lialve the 

 width of the slit A B. 



Next al'ter leaving AB sufficiently narrow that P' and S are 

 well separated, screw otf the l" objective and Substitute one of \" 

 or ^" . Observe that when focused the distance from centre of P' 

 to that of S remains the same, though botli of these are widened 

 out and the tendency to overlapping has therefore become increased. 

 Remove the objective and examine without any objective at all. 

 Still the same etfect is seen and the distance from centre of P' to 

 that of S is approximately as before. ' Continuing our experiment, 



15. 



16. 



we use the l" objective again and leaving ^4 i? as it was, gradually 

 opeu the slit P and observe how P' and S gradually overlap and 

 how the central portion of the band P' becomes more unifornily 

 illuminated thereby. Lastly repeat all the previous experiments using 

 white light instead of monochromatic , and when AB is suitably 

 narrow P' is seen white in the central part with the reddish 

 brown edges , and S and ?7 become complete spectra, violet ends 



^) Seeing that the point to wliicli tlie light from the slot converges 

 is a long distance oft" relatively to its width, the curvature of the wave 

 front over the width of the slot is very small, and does not ditfer appre- 

 ciably from the curvature of the wave front impinging on it , if no lens 

 is interposed, notwithstanding that in the latter case the wave front is a 

 divergent one. 



Zeitschr. f. wiss. Mikroskopie. XIX, 1. 2 



