429 



The President thought this instrument possessed many pro- 

 perties which were very desirable in one which was wanted to 

 be carried about, and there could be no doubt as to its excellence 

 of construction. 



Mr. Rheinberg read a note "On the Imitation of Polarisation 

 Effects by Diffraction," in w^hich he described the effects to be 

 obtained by placing a fine ruled grating of, say, 2,500 lines to the 

 inch, placed in the microscope above the objective. 



Mr. E. M. Nelson said that devices of this kind had often been 

 shown before in a very pretty manner, but hitherto without any 

 practical utility, but in this paper Mr. Pheinberg had placed the 

 idea before them in a manner which seemed likely to be of value. 



Mr. Karop inquired how the grating was put over the objective, 

 and whether it was necessary for it to be of any particular width, 

 or fineness of ruling ? 



Mr. Pheinberg said it w^as not necessary for the ruling to be 

 of any special width, although the fineness of the lines determined 

 the quality of the colours. The grating was ruled upon a small 

 circle of glass and laid upon the upper end of the objective. It 

 ne^d not be very wide, as the pencil of light at that point was so 

 small in diameter. 



Mr, Morland asked if by this arrangement polariscope effects 

 could be obtained upon objects w^hich would not polarise other- 

 w^ise. Would it give them, for instance, on crystals belonging to 

 the cubic system ? 



Mr. Pheinberg said it was not a polariscopic effect at all, and 

 could only be used to any advantage upon opaque objects. 



The thanks of the Club were voted to Mr. Pheinberg for his 

 paper. 



Mr. T. B. Posseter read a paper '' On the Anatomy of Dicrano- 

 tcenia coi'omda," a tapeworm unknown to the older helmin- 

 thologists, but originally discovered by Dujardin at Pouen, and 

 more recently found by himself in the intestine of a duck. The 

 subject was illustrated by diagrams and specimens shown under 

 the microscope. 



The President said it was always a pleasure to listen to a paper 

 which bore the stamp of originality, and certainly this seemed 

 to him to be a masterpiece of research. He hoped some one 

 acquainted with the subject would favour them with some 

 remarks upon it. 



