INVERTEBRATA. CRYPTOGAjMIA, jnCROSCOPY, ETC. 



1081 



Fig. 143. 



tive of the form recently constructed ])y Mr. Tolles, lines 30,000 to 

 the inch, ruled on a polished steel surface, are resolved with the 

 greatest ease." 



Professor Rogers also refers to a " comparator " which he has 

 designed as an improvement upon that described at p. 947 of vol.ii., a 

 description of which we defer until a detailed account, with a draw- 

 ing, has appeared. 



Mirror for Illuminating Opaque Objects for the Projecting 

 Microscope.* — Tlie subject of this note, by Mr. P. Frazer, jun., 

 (which we give verbatim) " is an arrangement for representing opaque 

 objects through the gas Microscope, especially adapted to Zentmayer's 

 Iji-inch objective. It is only claimed to be better than the para- 

 bolic reflector of Smith and Beck, 

 J. Lawrence Smith, Sorby, and 

 others, where the working distance 

 of the Microscope is comparatively 

 large (i. e. the distance from the 

 objective to the object on the stage 

 is i inch or more) and for the 

 purposes mentioned. Where the 

 distance is as great as that just 

 mentioned, the dispersion of rays 

 from the reflection at one point, of 

 rays from very different parts of 

 the mirror, is so great that only a 

 few rays from the upper part of 

 the mirror reach the lens at all. 

 It would be different with a lens 

 having a very small working dis- 

 tance, and in this case a parabolic 

 reflector would be preferable. 



The apparatus consists of a 

 brass tube made to slide over the 

 lens, on the lower end of which is 

 fixed a glass plate about 1 mm. in 

 thickness, so attached as to be 

 capable of a sliding motion to- 

 wards or away from the hinged 

 mirror which is attached to the 

 edge of the metal flange in which 

 the glass plate slides. This simple 

 contrivance porniits the glass plate to be brought into close contact 

 with the rtflf'cting mirror, no matter at what angle the latter may bo 

 placed. 



The mirror is made of nickol-platcd German silver neatly mounted 

 on a small hinge. 



The liglit is admitted from Ixlow through a diapliragni aftt>r the 

 rays have been rendered parallel by the condenser of the lantern, the 



• ' Vroc. Am. Phil. Sfw-. riiiln.,' xviii. (ISSO) |.. .'■>03. 



G V, cover-n;la.'«8. BF N. rt fleet- 

 ing mirror. U 1' K, reflcctidii on object. 

 L', raj'H which pass througli the oltjoc- 

 tivc. D, leiiH. T, sliding tube carrying 

 roflecting mirror. Angle of inoitlenc« 

 G2°. 



