XIX, 1. Rheinberg: Common Bcasis ofthe Theoreis ofMicroscopic Vision. 23 



(leduce from this that the ceutres of tlie bands from one auother 

 Vary inversely as tlie distance separatiug the slots, and we then more 

 clearly see the rehitionship both as to result and cause, to the case 

 of the extension or contraction of the bands formed from a siugle 

 slot, with which we fully dealt in the previous chapter. 



We have only spoken thus far of the rearrangement of light 

 of the central band from a Single slot. Natnrally the bauds 

 flanking this one also get broken up in like manner, but it is to 

 be noted that with these only half as many maxima of light are 



2t 



formed on each side of their central point, owing to the faet that 

 the central band from a Single slot is twice as wide as the other 

 ones (see fig. 7). ^ 



1) This pcculiarity that tlie central band of a single slot is twice as 

 wide as the others is worthy of notice. It may be looked upon as diie 

 to the foUowing reason: With Single slots we have seen that we get our 

 brightest light at all points at which rays arrive from the two ends of the 

 slot with a difference of an odd number of half wave lengths, and that 

 from these points the light gradually decreases tili the nearest point in 

 the same plane at which they arrive with a diflference of half a wave length 

 more, or half a wave length less. But there is one exception, viz. : l)e- 

 tween the point Q where there is a difference of one half wave length, and 

 P' where there is a ditference of no half wave length, for from Q to P' 



