86 MEMOKANDA. 



extreme oblique light, that only one-half of the field of view 

 of the microscope was illuminated ; the line of demarcation 

 between the illuminated part of the field and the black-ground 

 part, passing directly through the centre of the field, and this 

 division of the field remained constant when no slider was on 

 the stage, when the one with the objects mounted dry was 

 placed there, and when the one with the balsam-mounted 

 objects was used. Had the angle of aperture been at all 

 altered or lessened, by the interposition of the sliders, it must 

 instantly have become visible l3y the change of illumination 

 in the field of view of the microscope. 



When I first read the account of the results obtained by 

 Professor Robinson and Mr. Wenham, it struck me forcibly 

 that they must have committed some great error ; for, in 

 experiments with the fine linear objects, I had never been 

 able to see the markings on the JV. rhomhoides with an aiigle 

 of less than 120°, when it was mounted dry : now, if it cannot 

 be seen with less than 120^ when mounted dry, it would be 

 impossible with any angle to see the markings on it when 

 mounted in balsam ; as an angle of 150^ (according to the 

 results given in your Journal) would be reduced to less than 

 80° when employed to examine an object in balsam ; but in 

 opposition to this, I always consider that with my l-12th of 

 150° of aperture, I can see the markings on N. rhomboides 

 better in those specimens which I have in balsam, than in 

 those which are mounted dry ; and Mr. Wenham himself 

 stated to me that he had never seen the markings on N. 

 rhomboides so well as he saw them on one of my dry speci- 

 mens, and yet at least they are equally as distinct on those 

 which I have in balsam. I should advise both Professor 

 Robinson and Mr. Wenham to go over their experiments 

 once more, and I think they will be able to determine how 

 they have fallen into error. — J. D. Sollitt, Gi'ammar- School, 

 Hull 



Illumiiialiou of Microscopic Objects. 1 beg permission tO 



insert in the next number of the ' Quarterly Journal of Micro- 

 scopical Science' a short comment on Mr. Rainey's remarks on 

 my paper on microscopic illumination. I have no desire to 

 raise a controversy that must in the end be perfectly useless, 

 but as Mr. Rainey misquotes my sentences, and implies that 

 I am " dogmatical," a few words in reply may perhaps be 

 allowed, with the understanding that I feel all due deference 

 and respect for Mr. Rainey's long experience as a micro- 

 scopical observer. 



In till? first place, where can be the " ambiguity and com- 



