ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 321 



At present the objectives are not on sale, but it is expected that 

 very shortly both objectives and glass can be purchased in the 

 usual way. 



Mr. E. M. Nelson, who has had our objective under examination, 

 writes as follows : — 



" The great benefit which will accrue to microscopists from the 

 use of lenses of this construction will be due, not so much to the 

 absence of colour as to the greater freedom from siDherical aberration. 

 In other words, these lenses will stand illuminating by axial cones of 

 larger angle. This is evident from its performance on Navicula 

 rhomboides (Cherryfield). This diatom, which under oblique light is 

 a test for a 1/4 of 90°, becomes a pretty severe test for the widest- 

 angled homogeneous-immersion objective under a large axial cone ; 

 in the former case only crossed strife, or checks could be made out, 

 but in the latter the minute grating should be clearly seen. 



This minute grating I have never seen so sharply defiined as 

 with this new objective when illuminated by Powell's achromatic 

 condenser with full aperture. It shows the following very delicate 

 objects most distinctly : fracture through the delicate perforated mem- 

 brane inside the large areolations in Isthmia nervosa, and the fracture 

 through the still more minute perforations inside the hexagonal 

 structure of Triceratium favus. This last object may be termed the 

 highest test to which the ' microscopy ' of the present day can be 

 subjected. Those interested in oblique light will be glad to hear 

 that the strife on A. pellucida come out sharper than I have ever 

 seen them before. The valve is resolved from tip to tip, showing 

 that the lens is flat in its field. To sum up, this lens is decidedly 

 the most brilliant objective I have ever seen. . . . After mentioning 

 the above tests, it is almost imnecessary to say that bacteria, stained 

 and mounted in balsam, are most clearly defined." * 



Mr. Nelson subsequently wrote us that he had discovered a very 

 minute perforation on the interior lining membrane of Etipodiscus 

 Argus. This diatom consists of two separate membranes. The 

 outer one has a brown tint with transmitted light, but appears white 

 and sparkling, not unlike loaf sugar, with reflected light. This outer 

 membrane has large and for the most part oval areolations all over 

 it, the interspaces being granulated. The inner membrane, which 

 is very transparent, has rows of comparatively large white dots 

 radiating from the centre of the diatom. The whole of this inner 

 membrane between these white dots is covered with very minute 

 perforations. These perforations are often arranged in circular rows 

 round the white dots, and are, in reality, " tertiary " markings. 



There is, so far as he is aware, no record of a " tertiary " marking 

 on a diatom having been observed before. 



Liquid Lenses.* — Herr P. Lebiedzinski has described some liquid 

 lenses prepared by a method devised by Herr K. Lochovski and 

 himself. 



* Engl. Mech., xliii. (1886) pp. G2-3. 



t Medical Society of Warsaw, 1881, p. 379. Reported iu Jahresber. iiber die 

 Fortscliritte dor Anatomie und Physiologie, r. (1882) p. 6. 



Ser. 2.— Vol. VI. " Y 



