512 SUMMARY OF CURRENT RESEARCHES RELATING TO 



affected :it all, so that only transparent or fairly translucent minerals 

 yield any effects ; in addition, they must be more or less distinctly 

 coloured. The number of minerals suitable for microspectroscopic 

 study is therefore rather limited, but the fact that the specimens need 

 not be scratched, broken, or altered in any way renders the method of 

 considerable use in the identification of crystals too valuable to be 

 broken up for the usual tests. Even when other methods are applicable, 

 i he spectra may serve as confirmatory tests. The author discusses in 

 detail the spectra of the rare-earth minerals, the uranium metals, and the 

 garnet group. He tabulates the result of the microspectroscopic examina- 

 tion of about 200 minerals. 



(2) Eye-pieces and Objectives. 



Novel Pseudoscopic Eye-piece.* — J. Strong discusses a rough-and- 

 ready pseudoscopic eye-piece which gives very beautiful and striking 

 effects. A cardboard or stiff paper tube, 2 in. long, is fitted on to the 

 outside of the draw-tube of the Microscope. Outside this is another 

 tube, 7 in. in length, sliding somewhat stiffly and carrying at its upper 

 end a diaphragm with a f-in. aperture. The short inner tube carries 

 at its upper end a single meniscus lens, fixed convex side uppermost, and 

 of focus about 4 in. This particular lens has nearly all the faults a lens 

 can have, but the designer thinks that the pseudoscopic effect is due 

 to these very faults. The insides of the tubes should, of course, be 

 blackened. With this simple apparatus the author gets magnificent views 

 of Foraminifera, Radiolaria, Rotifers, and all large "binocular" objects. 



Zeiss' " New " Object-glass. | — With reference to this auxiliary, 

 which was described by E. M. Nelson in the November number of the 

 Journal of the Quekett, and noticed in this Journal in April last,! 

 J. W. Gordon points out that the lens is not so novel as Nelson supposed, 

 inasmuch as one of identical design was made in 1909 by Messrs. 

 R. and J. Beck to Gordon's order, and was exhibited at the Optical Con- 

 vention in 1912, and was fully described in the Convention Catalogue. 



In the same paper the author points out the advantage to be 

 gained by the following extension of the principle involved in the con- 

 struction of this lens. He mounts a hemispherical lens on a cover-glass 

 enclosed in a shallow brass ring, which enables the observer to move the 

 whole article about and place it where required ; it thus functions to 

 some extent as a finder. If, now, the specimen with this supplemental 

 lens be brought into position under a dry objective, a combination is 

 obtained precisely such as Nelson desires. It will be noticed that it is 

 not necessary to make any corrections for colour or for spherical aberra- 

 tion, because if the lens is of the right thickness, so that the centre of its 

 spherical surface coincides with the focal point, then the incident beam 

 passes the air-glass surface of the lens without refraction, and therefore 

 without aberration of any kind. The cost of the auxiliary would be very 



* English Mechanic, ci. (1915) pp. 536-7 (1 fig.). 



t Journ. Quekett Micr. Club, xii. (1915) pp. 515-20 (2 figs.). 



t Pages 178-9. 



