Coscinodiscus asteromphalus. By T. W. Butcher. 727 



Mr. Firth has mounted them so well that many dozens of photo- 

 graphs have been taken from them without disturbing them in the 

 slightest degree. 



There is here material in every way fitted to display the new 

 structure described by Mr. Nelson, for surely, if present, it would 

 be apparent and demonstrable under critical light ; and if a 

 structure, and constant, it should not be able to defy detection. 

 Every effort has been made to discover the presence of this 

 membrane, for it was felt that if once seen, a photomicrograph of 

 it could be secured, and that would be all the evidence required in 

 confirmation of Mr. Nelson's announcement. The failure to pro- 

 duce this print arises from the circumstance that I have not been 

 able to get a "glimpse " even of this problematical membrane. 



Series V., VI, and VII., showing Tertiary Markings. — 

 Arising out of the resolution of these tertiary markings is a 

 question of considerable importance to all microscopical students. 



In the Eoyal Microscopical Society's Journal, 1910, p. 147, 

 Mr. Nelson states " a definite case." The words are : " The speci- 

 men, the Microscope, the sub-stage condenser, the lamp, the method 

 of work, and the eye at the eye-end (hardly improved for being 

 twelve years older), were all the same," and " this apochromatic 

 |- is more sensitive to tube-length, stands a larger axial cone, 

 bears a deeper eye-piece, and has sharper definition than any 

 Microscope lens I have yet seen." In short — the lens is the 

 finest Mr. Nelson has, as yet, seen, and " a step forward in the 

 perfecting of the apochromatic has been accomplished." It is " a 

 new lens," in our sense of the word, and, in fact, the note on 

 page 698 commences thus : " Additional work with the new lens 

 mentioned in my last note." Therefore one need not dwell on the 

 absurdity of supposing that Mr. Nelson has written and the 

 Society has published his critique on a lens that he had just 

 recently happened to buy. 



At the 472nd Meeting of the Quekett Club (March 28th, 1911), 

 reported in the English Mechanic, the official organ of the fort- 

 nightly Meetings of that Society (No. 2402, p. 215), a paper* was 

 taken as read, in which Mr. Merlin says, " that in 1899 he obtained 

 a Zeiss \ apochromatic of measured N.A. 1 '42, and initial magnify- 

 ing power 87. He had reason to know that this objective was then 

 probably second to none in existence. However, early in 1910, he 

 was informed that a further advance had been made in the con- 

 struction of these lenses, and he obtained an example of the com- 

 bination in June of last year. This objective, exactly similar in 

 aperture and power to the older one, has been found to afford 

 decidedly superior defining power and contrast on delicate objects. 

 Subsequently he re-examined many objects familiar to him with 



* Journ. Quekett Micr. Club, Series 2, ix. p. 199. 



