24 



J. RHETNBERG ON AN OVERLOOKED POINT CONCERNING 



parallel light through them? The humps a, b, and c ol the 

 intensity curve will remain, but they will be steeper, and there 

 will be a tiny negligible hump between them. 



And for every extra slot we add, we get extra tiny little humps 

 (secondary maxima) between the large humps or chief maxima 

 a, b, and c. These remain in the same position whatever the 

 number of slots, but they get steeper and steeper. After six or 

 seven slots their sides are almost perpendicular (Fig. 5).* 



Jflany Slqts 



Reverting to Abbe's generalisation, he showed that the condition 

 necessary for resolution of the slots or lines was fulfilled when, 

 and only when, the objective had a sufficiently wide angle to grasp 

 two of these large humps or chief maxima. They bear what is 

 known as a phase relationship to one another ; in other words, 

 the ether particles which are swinging to and fro whenever light 

 is passing, happen to be just swinging in unison at the centre of 



* Simple detailed explanations as to the formation and changes in the 

 appearance of these maxima are given in my article, " The Common 

 Basis of the Theories of Microscopic Vision treated without the aid of 

 .Mathematical Formulae," in the Zeitschrift fur wis sen sell aftliche 

 Mikroskopie, vol. xix. Reprints obtainable from Williams & Norgate, 

 14, Henrietta Street, London, W.C. 



