226 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



half-plate dark slide A. B is a pair of light brass chains "which engage 

 with hooks on the opposite side of the frame, and by which the camera- 

 bellows may be supported when not in use. C is the brass union between 

 the eye-piece and the bellows ; D, two guides into which the base of the 

 Microscope fits. 



Hekschel, Sik W. J. — Colour Photography. 



[Gives a sketch of Ives' and Sanger Shepherd's methods.] 



Brit. Joum. of Photorj,, July 12, 1001. pp. 439-41 (3 coloured pis.); 

 Ann. Hep. Smithsonian Institute, 1901, pp. 313-6. 



(5) Microscopical Optics and Manipulation. 



Leiss' New Crystal Refractometer for the Determination of 

 the Refractive Index of Large and Microscopically Small Objects.* — 

 This instrument, designed by C. Leiss, is intended to apply to small 

 crystals, as well as to mineral plates enclosed in thin sections. It may be 

 considered as an improvement of the refractometer of C. Klein.t Two 

 essentials of construction are : — (1) The association of the instrument 



Fig. 43. 



with a Microscope ; (2) the stopping-out of all disturbing light. The 

 Microscope (or telescope) is shown in fig. 43 ; for convenience of obser- 

 vation it is made with an elbow. Ob is the objective whose focal plane 

 is marked X ; Oc is the single-lens ocular ; P, the totally reflecting prism ; 

 N, a nicol which can be inserted at pleasure and can be rotated by a 

 small knob ; J is the iris diaphragm placed at the Ramsden circle of the 

 ocular ; L is an observation lens, as recommended by Czapski and Pulfrich, 

 formed of two lenses, adjustable in a sleeve and, by means of a hinged 

 arm, quickly applied to the iris or removed. The lens c in front of 

 objective Ob is the well-known correction lens, which parallelises the 

 beams emergent from the hemisphere, The application of the loup L 

 makes the telescope into a Microscope of small magnification, and with 

 it the preparation can be viewed not only from above (through the air) 

 but also from below (through the hemisphere). A proper selection of 

 lenses enables this to be done without special correction or change in 

 the adjustment of the Microscope. When the loup L is removed, the 

 telescope gives a magnification of lj ; when the loup is applied the 



* Zeitschr. f. Instrumentenk., xxii. (1902) pp. 331-4 (3 figs.). 

 f S.B. Beil. Akad., 1902, pp. 113 and 653. 



