PROCEEDINGS OF THE SOCIETY. 761 



Mr. W. E. Traviss, in further reference to the subject, showed by 

 drawings on the l)oard how the blades of these scissors were modified 

 to answer the purpose required, enabUug them to hold the piece of 

 weed quite firmly first, and to cut it afterwards. 



The Chairman thought this little instrument was likely to be 

 extremely useful to the many microscopists interested in pond life, and 

 proposed the thanks of the Society to those gentlemen who had brought 

 it under notice. 



Mr. A. A. C. E. Merlin's paper " On Ghost Images seen in the 

 secondaries of Coscinodiscus Asteromphalus,^'' was read by Dr. Hebb. 



The Chairman said it was a matter of regret that the author of this 

 paper was not able to be present to read the paper himself. The 

 subject-matter was extremely interesting, and he should be glad to bear 

 any remarks upon the opinions expressed in the communication. 



Mr. Beck said there was one point which might be inferred from 

 the paper which was probal)ly not intended to be conveyed l^y 

 Mr. Merlin, and that was as to the advantage of the use of very high 

 eye-pieces under ordinary circumstances. No one should think of 

 using a 1-inch objective with a high eye-piece in order to make it do 

 the work of a j-inch, it being well known that high eye-pieces could 

 only be usefully employed with high-angled olijectives, and the advan- 

 tage of high eye-pieces only commenced when used with lenses of high 

 power and maximum aperture. He thought that in dealing with such 

 subjects too much stress was often placed on resolution, which only 

 applied to objects which possessed a regular structure ; there was much 

 yet to be learned as to the limits of visibility of objects with irregular 

 structure. Several papers had been read before the Society showing 

 that whilst a single line could be easily seen, it was a much more diffi- 

 cult matter to resolve a number of such lines when close together. In 

 drawing attention to the advantage of high magnifying powers in the 

 cases mentioned Mr. Merlin had done a useful service. His experiments 

 with low power objectives were valuable by way of illustration, but could 

 scarcely be recommended in themselves for practical observations. 



Mr. J. W. Gordon said that there was another advantage of high 

 magnifying power of which he did not remember having seen any notice 

 in Mr. Merlin's paper or elsewhere. It was due to the circumstcince that 

 every lens produced not a simple plane image, but a solid image of the 

 structure on the stage. In the case of objects like diatoms, where they 

 had various structures lying close together one beneath another, it was of 

 importance to be able to separate these in the eye. By means of a 

 drawing on the board, Mr. Gordon showed that if the object under 

 view was a cube, a solid image of this would be formed in the eye 

 having a certain depth along the optical axis proportionate to the 

 magnification. The position of this solid image iu relation to the plane • 

 of the retina could be altered if it was wished to see what lay in any 

 particular plane. If they had two sets of markings on the cube, one on 

 the top and the other on the bottom, they must have them sufficiently 

 far apart for one set to lie clear of the sensitive region of the eye if 

 they wished to see the other set distinctly, and to get the top and 



