PBOCEEDINGS OF THE SOCIETY. 731 



room and with strong illumination on the point, it was only possible 

 to obtain a faint image with so much diffused light around them as 

 tbere was under present circumstances. All tbe Microscopes were fitted 

 with Tj-in. objectives, and the points in the case of the first two were 

 produced by very small apertures in pieces of tin-foil, the others being 

 light reflected from small mercury globules. Under the first Microscope 

 the point of light was viewed with the ordinary aperture of the object- 

 glass. The second had only a small aperture, and instead of seeing a 

 copy of the point they got a large disc. The third had a slit aperture, 

 and the image of every point was a slit with a series of diffraction 

 images on either side. The fourth had a triangular aperture, and this 

 showed a single point in the centre and a series of six star-like rays. 

 The fifth had three small holes, the result being a series of images ar- 

 ranged round a central disc ; and the sixth was viewed through a grating, 

 and showed a small point image with two slit-like flunking images. The 

 use of this demonstration was to illustrate how profoundly the images 

 shown by the Microscope were influenced by the shape of the apertures 

 through which minute objects were seen. With greater brilliancy of 

 illumination many more diffraction images could be seen, outside those 

 which were only faintly shown under present conditions. 



The President said he was very glad that Mr. Beck had taken the 

 opportunity of explaining more fully what was to be seen upon the 

 t ble, as it would enable the exhibition to be more greatly appreciated. 

 The fine adjustment of the Microscope he had shown them was ex- 

 tremely ingenious in its design, and would, no doubt, be found of great 

 advantage in practice. 



Mr. J. W. Gordon said he had listened with great interest to Mr. 

 Beck's explanation of the demonstration he had prepared, but personally 

 he was so extremely anxious to see the examples for himself —and had no 

 doubt that many others also were equally desirous of doing so — that he 

 had no idea of interposing any lengthened remarks of his own upon the 

 subject. There was, however, one thing which struck him very specially 

 in connection with it, and he should like to say just a word or two about 

 that. There could be no doubt that the experiments would demonstrate 

 the existence and appearance of the antipoint in each case, and the 

 importance of this could not be over-estimated ; but after all, it was clear 

 that the results had been produced by very special apertures which it 

 wonld not be possible to use in an ordinary instrument for ordinary 

 working purposes. There was, however, another and equally important 

 image which he should like to see, and that was the antipoint which was 

 formed in the eye, and he hoped tbat some day Mr. Beck would be able 

 to bring down a demonstration of that ; for however interesting and 

 instructive the study was of the antipoints which were formed by 

 diaphragms, he thought it was a great deal more important for them to 

 understand the nature and effects of the antipoints formed by the eye. 

 The subject of the antipoint formed in the instrument had been examined 

 very successfully, but the question of the antipoint in the eye had 

 almost escaped the attention of those who had been engaged in that 

 class ( >f research. 



The President expressed his sense of the value of Mr. Gordon's 

 explanations. During Mr. Beck's interesting exposition of his exhibition 



