Physics. — ''On the dif Taction phenomenoji caused hy a great 

 number o f irregularly distributed apertures or opaque particles" . 

 B}' Dr. W. J. DE Haas. Communicated by Pi-of. H. A. 

 LoRENTZ. (Communication from the physical laboratory of 

 Teyler's Institute). 



(Communicated in the meeting of December 29, 1917 i)). 



1. When before the objective of a telescope focussed on a distant 

 lightpoint, we keep a screen, containing a great number of irregu- 

 larly distributed equal circular apertures, we observe a well-known 

 diffraction phenomenon. It will be known that the same phenomenon 

 is observed when the investigation is made with a transparent screen, 

 covered with opacpie corpuscles wiiich correspond to the above men- 

 tioned apertures, e.g. a glass plate strewn with grains of lycopodium. 

 The diffraction image consists of a light central spot and round this 

 the rings which would be found in the case of one single aperture; 

 we now see however fluctuations in the intensity which we can 

 best describe as a fibrous radial structure. Von Laue ") investigated 

 this phenomenon, and came to the conclusion that it could not be 

 explained by classic optics. In this communication the considerations 

 will be discussed which made me doubt the righlness of this con- 

 clusion. First I want to stipulate however, that I have not any 

 objection to von Laue's theoretical considerations on the diffraction 

 phenomenon by monochromatic light '). 



2. My diffeient investigations will only shortly be discussed. I 

 confined myself to visual observation. The diffraction phenomena 

 were studied in two different ways. First I worked with turned 

 copper rings over which thin paper impregnated with indian ink had 

 been stretched, when still wet. 



^) The essential contents were read in the meeting of Sept. 29, 1917. 



2) M. V. Laue, Die Beugungsersclieinungen an vielen nnregelmassig verteilten 

 Teilchen, Sitzungsber. Akad. Berlin 1914, p. 1144; Mathematische Belrachtungen 

 an vielen nnregelmassig verstreuten Teilchen, Mitteilungen. Phys. Gesellsch. Zurich, 

 1916, p. 90; Ein Versagen der klassischen Optik, Berichte deutsch. physik. Ges. 

 18, p. 19, 1917, 



^) See H. A. Lorentz, Zittingsverslag Dec. 1917, p. 1120. 



