ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



515 



room the projection of microscopic preparations, lantern slides, or of 

 photographic negatives may be easily traced, and a glance at the illus- 

 tration will show the simplicity of the construction. A, shown also in 

 end section at A', is a piece of wood 2 x 2 in. and about 3 ft. long, 

 grooved by means of a rabbet plane, so as to clamp firmly to the lantern 

 table (see A'). The arm B bears the two grooved strips C, which carry 

 at an angle of 45° the mirror D. This casts the image on the drawing 

 surface E, where it may be traced with ease. The magnification depends 

 directly upon the distance of the drawing-board from the mirror. Thus 

 if the enlargement is two times when the line E-D is 10 in., the image 

 will be enlarged four times if the line E-D is 20 in. Magnification 

 also depends upon the distance of the mirror from the lens. 



Direct-vision Prism and Apparatus for the Projection of Spectra 

 and for Illumination with Spectral Light.*— J. Koenigsberger 

 describes under the above title the fluid prisms made by the firm of 

 F. Hellige and Co., of Freiburg, Breisgau. He recommends them as 

 superior in cheapness and efficiency to any others, and as more adapted 

 for projection. 



Illuminating Arrangement for the Metal-Microscope.t — W. v. 

 Ignatowsky draws attention to the difficulty of effectively illuminating 



*-B 



the object in high-power metallography, and points out that illumina- 

 tion must therefore be through the objective. Reflections at the back 

 surfaces of the constituent lenses, however, interfere with the object, 

 and, although these reflections can be to a certain extent cut out by a 

 stop, the manipulation is tedious and difficult. The author suggests, 

 therefore, the arrangement shown in fig. 77. B is the light-source ; J, 

 an iris ; L 19 a small lens ; M, the metal object ; 0, the objective ; L, the 

 back lens ; and P the prism. This prism, P, is rotatory about a 

 perpendicular axis, and can also be moved backwards and forwards 

 along A B. The result is that, when the iris-opening is reduced, any 



* Zeitschr. wiss. Mikrosk., sxv. (1909) pp. 2S7-8 

 t Tom. cit., pp. 434-8 (3 figs.). 



2 M2 



