462 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



Latteux, p. — Manuel de Technique Microscopique. (Manual of Microsc.ipicul 

 Technique.) 

 [Cf. infra, (1). In addition to Technique, it contains chapters on Simple and 

 Compound Microscopes, Accessories, Test Objects, Micrometry, Drawing, and 

 Photomicrography.] 



3rd ed., xvi. and 820 pp. (385 &^s. and 1 pi.), 8vo, Paris, 1887. 

 Powell's (T.) Microscope and Appendages " made out of odd materials of various kinds." 

 (Mr. Powell is a shoemaker.) 



Proc. Lit. and Phil. Soo. Liverpool, No. XXXIX. (1885) p. xlviii. 



(S) Eye-pieces and Objectives. 



Apochromatic Objectives.* — Dr. M. D. Ewell has examined a Zeiss 

 apochromatic objective, 1/12 in. N.A. 1-40 (with eye-pieces), made from 

 the new optical glass. By oblique light he considers it is a well-corrected 

 objective, but no better than first-class American objectives, except that the 

 images have hardly any perceptible colour. With axial illumination, 

 however, using an Abbe condenser of N.A. 1-40, with no stops or 

 diaphragms whatever, the real superiority of the glass becomes apparent. 

 " I have never before seen so clear and perfect a picture under similar 

 conditions ; and it is clearly apparent that the corrections are approxi- 

 mately perfect up to the extreme limit of its aperture. It is not difficult 

 with such axial illumination to resolve a Moller Probe-Platte from end to 

 end, and the images are practically colourless. In the present state of our 

 knowledge, this objective certainly leaves nothing to be desired. The 

 working distance is large, about 1/100 in., and the so-called searcher eye- 

 pieces make even as high a power as a 1/12 very convenient in use. I do 

 not assume to speak for any one but myself ; but such, as it seems to me, 

 must be the judgment of any unbiassed observer. For the practical worker 

 with axial illumination, it seems to me that the apochromatic objective is 

 destined to become the objective of the future." 



Double Objectives with a common field of view-j — These (made by 

 Herr H. Westien) consist of two lenses or lens-systems, which having been 

 ground away at the edges on one side are placed so near and under such an 

 angle to each other that their optic axes coincide with the axes of the eyes ; 

 when this is the case the two fields of view appear united into a single one. 



(8) Illuminatingr and other Apparatus. 

 Hilger's Opaque Illuminator. — For the illumination of opaque objects 

 to be viewed with Campbell's Micrometer-Microscope, Mr. A. Hilger has 



devised the apparatus shown in 

 Fig. 102. fig, 102, which is a modification 



wr/i^ axis, and by means of an adjusting 



screw this angle may be altered a 

 few degrees, so that the object may be illuminated from one side only if 

 required. A system of condensing lenses with rack-work is applied to 

 direct the light from the external mirror to the speculum, whence it is 

 reflected through the objective and condensed upon the object. 



* The Microscope, vii. (1H87) p. 6:S. 



t Cential-Ztg. f. Opt. u. Mech., viii. (1887) p. GO. 



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