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A Paper read lefore the Bristol Microscopic Society y 1 876. 



BY H. E. FRIPP. 



THE following account of Professor Abbe's method of 

 demonstrating diffraction spectra in the microscope will, 

 it is hoped, prove acceptable to the student and practising 

 microscopist, as well as to those who are specially interested in the 

 optical theory by which these demonstrated facts receive their 

 explanation. This theory is stated and illustrated in simple and 

 intelligible form in a preceding article, in reference to which the 

 translator thinks it proper to remark, that the admirable account of 

 interference phenomena given in Chapter III. of the Treatise on 

 the Microscope, by Professor Naegeli and Schwendener, includes 

 the consideration of various other forms and causes of diffraction 

 spectra which equally require the attention and study of the 

 scientific microscopist, but of which want of space forbade further 

 notice at present. The particular case which has been discussed 

 in |the pages translated is, however, by far the most important, as 

 being the key to the proper understanding of all images of the 



