736 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Cheshire's Apertometer.* — This instrument (fig. 119), made by 

 R. and J. Beck, consists of a glass disk with a series of concentric rings 

 in its lower surface. The object-glass to be tested is focused to a mark 

 on the upper surface, and, the eye-piece having been removed, the 



Fig. 119. 



Fig. 120. 



number of rings seen in the back lens of the object-glass gives the aper- 

 ture in decimals, each ring denoting • 1 N.A. 



For high powers, when the lens is small and the rings difficult to 

 count, a special eye-piece (fig. 120), which focuses to the back focal-plane 

 of the object-glass, is required. This is inserted in place of the usual 

 eye-piece. 



Edinger's Drawing and Projection Apparatus. — This apparatus, 

 which has more than once been noticed in our Journal, f has been 

 recently revised and improved.:]: It is shown in figs. 121-125, of 

 which fig. 122 illustrates the principles of construction and is lettered for 

 reference. The apparatus is primarily intended for facilitating the 

 work of preparing drawings of microscopic objects and is available for 

 comparatively high magnifications. To this end the image of the object 

 is projected directly upon the drawing surface where it may be traced 

 with a lead pencil. The instrument is likewise adapted for demonstrating 

 to a small audience objects on the screen and for photomicrography. 

 The apparatus consists of a cast-iron column S mounted upon a rect- 

 angular frame in which the drawing-board Z is made to slide in or out. 

 The column S is provided with a guide-bed along which the entire 

 optical outfit, together with the lamp, can be made to slide up and down 

 after loosening the screw R. The movable part B has Hkewise guide- 

 bars for the independent displacement of the lamp L, object stage 0, 

 and lens-holder H. The lamp, together with the condenser K, may be 

 displaced along the optic axis by means of the handle G. The object 

 stage may be raised or lowered, as required, according to the objective 

 used, and its position is shown on a scale divided into i cm. The 

 lens-holder H remains fixed at a distance of 1 cm. from the lower end of 

 the guide-bar, and should not be detached excepting during the removal 

 of the apparatus. The object-stage canies the condenser K2. The 

 latter consists of two lenses, either of which may be employed separately, 

 in addition to which the condenser may be swung aside. The iris dia- 



* R. and J. Beck's Catalogue of Microscopical Apparatus, 1907, p. 6. 

 t See this Journal, 1905, p. 650; 1891, p. 811. 



X Zeitschr. wiss. Mikrosk., xxiv. (1907) pp. 26-34 (5 figs.). See also Leitz' 

 Special Catalogue (Wetzlar) English edition. 



