1901] MICROSCOPICAL JOURNAL 259 
special general meeting several alteratious in the by-laws 
were put and agreed to unanimously. At the ordinary 
meeting Mr. T. H. Powell exhibited Coscinodiscus aster- 
omphalus under a new 1-40 inch apochromatic oil-immer- 
sion objective; Mr. J. W. Gordon read a paper entitled 
‘An Examination of the Abbé Diffraction Theory of the 
Microscope,” in which he stated that the above long- 
accepted explanation of the phenomena of high-power 
microscopic observation had been adopted on insufficient 
proof, and would not bear the test of critical examina- 
tion. The Abbé theory claimed that pictures formed by 
the microscope of very minute objects were due to dif- 
fraction images originated by the object, and that when 
the oblique rays of light by which these diffraction im- 
ages existed were excluded no image of the object was 
possible. This theory had been experimentally illus- 
trated by Professor Abbé by means of a grating on the 
stage of the microscope and a series of diaphragms be- 
hind the microscope object-glass with slits to partially 
exclude oblique rays, Mr. Gordon showed that, although 
under such favorable circumstances diffraction effects were 
produced by fine objects on the stage of the microscope, 
these effects did notappreciably influence the form of the 
image. He also showed that the experimental results 
produced by the above-mentioned diaphragms, which 
were adduced to prove the theory, were due to a diffrac- 
tion effect produced by the diaphragms themselves, and 
not by the grating on the stage of the microscope, the 
same results being obtained with an aerial image of a 
grating projected upon the stage by a lens in place of the 
actual grating. He maintained that in the microscope, as 
in the telescope, it was necessary to eliminate diffraction 
effects as far as possible by making lenses of larger aper- 
ture, and not, as in Abbé’s theory, to include as many 
disffraction phenomena as possible. Diagrams in illus- 
tration of the paper were thrown upon the screen, and 
