JOUENAL 



OF THE 



ROYAL MICROSCOPICAL SOCIETY. 



DECEMBER, 1907. 



TRANSACTIONS OF THE SOCIETY. 



XIV. — Note on a New Prismatic Microscope Ocular. 

 By A. A. C. Eliot Merlin. 



{Bead October 16, 1907.) 



The writer has at various times been obliged to make prolonged 

 observations with the Microsicope in an upright position, and has 

 practically found that it entails great fatigue to the eye, especially 

 when examining rapidly moving infusoria under the highest powers. 

 It occiuTed to him that a comfortable posture when perforce using 

 the instrument upright could be easily secured by means of a 

 properly designed prism, to be placed over the eye-lens of the 

 ocular, and so constructed that the worker should view the image 

 bent to 60°, exactly as if the Microscope were inclined at that most 

 convenient observational angjle. 



On being applied to for assistance in this matter, Mr. E. M. 

 Nelson most kindly computed a prism of the kind required, and of 

 which a figure is subjoined. This prism has been constructed for 

 the writer by Zeiss of Jena, and has proved most efficient and 

 satisfactory in use. It has been adapted to the Zeiss x 12 long 

 tube compensating ocular, but yields good results also with the 

 X 18 and x 27 for the long tube, and with the x 4, x 8, x 12, and 

 X 18 compensating eye-pieces for the short tube. 



Applied to the x 12 ocular, it passes the full cone of the 

 12 mm. apochromatic objective of measured N.A. 0"7. This was 

 proved by arranging the iris diaphragm of the substage condenser 

 so that its edge should be just apparent at the back of the objective 

 when viewed without the eye-piece, the prismatic ocular being 

 then inserted and the Eamsden disk examined with a loup, when 

 the periphery of the diaphragm remained visible at the edge of the 

 Dec. 18th, 1907 2 u 



