SCO 



On Interference Phenomena in Relation to True and 

 False Images in Microscopy. 



By B. Thompson Lowne, F.R.C.S., F.L.S., &c. 



(Read January 25th, 1889.) 



Whilst we all admit that Professor Abbe has done excellent 

 work in elucidating a theory of microscopic vision, many of us 

 regret that he has apparently thrown a bone of contention in the 

 way of some of the most earnest seekers after truth. 



When our old friend and Vice-President, Mr. E. M. Nelson, 

 read his paper at the last meeting of the Society, I thought it was 

 high time that I should more fully study Professor Abbe's views, 

 and that I should settle, in my own mind at least, the question as 

 to whether my opinion or Mr. Nelson's was correct upon the subject 

 of diffraction phenomena. 



I am ready to confess that for some years past I have supposed 

 the question of diatom structure to be so inseparably connected 

 with diffraction phenomena that I entirely disbelieved it could 

 be definitely settled. I, however, set myself to work to consider 

 the effect of diffraction on the image, and I worked out, by the 

 usual formulas, the appearances which should occur in certain cases 

 if the images were false. Theoretically it appeared to me that the 

 various figures given of diatom structures depended on the aperture 

 of the objective; and that the progress of microscopical improve- 

 ment in this respect, with the increase of delineating power, sup- 

 posed by Professor Abbe to be due to diffraction, agreed in the 

 main with the altered diatom appearances recorded by successive 

 observers. 



I then took counsel with your Vice-President, and asked him to 

 show me some of his diatoms. You all know Mr. Nelson's skill 

 in this department, and I came from his house fully convinced that 

 he had shown me true images of actual structures. 



I felt strongly that the usual views with regard to Professor 

 Abbe's researches, in this country at least, needed revision, and I 

 half felt that the professor's chief supporters were dogmatizing on 



