B. T. LOWNE ON INTERFERENCE PHENOMENA. 



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a subject of extreme difficulty, which they did not entirely com- 

 prehend. 



I have read Professor Abbe's papers with great care, and 

 although I cannot quite fix the statement which has so frequently 

 been made — that the investigators of diatom structure and all 

 very minute objects are wasting their time — at Professor Abbe's 

 door, I feel this is the legitimate conclusion to be drawn from 

 the statements he makes. 



I. On Interference. 



Interference phenomena depend on the joint action of two light 

 waves . Of course, all the light waves which fall upon any surface 

 act jointly, but for the action to produce a visible result it must 

 continue for an appreciable time. The interferences which occur 

 from the joint action of two luminous bodies on any surface cannot 

 be perceived, because each sends vast numbers of waves in every 

 possible phase to the surface, in every second. 



If, however, we allow the light from a luminous point, say the 

 focus of a condenser, to fall upon two metallic mirrors, ABC 

 (Fig. 9), placed at an obtuse angle to each other, the pencil of light 

 L a B which falls on A B, is reflected upon the screen P Q, as if 



Fig. 9. 



