578 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Fig. 104. 



MICROSCOPY. 

 A. Instruments, Accessories, &c." 

 CI) Stands. 



Ordinary Microscope arranged for Axial Images of Doubly Re- 

 fracting Bodies.f— Prof. L. Dippel, after referring to the importance of 



applying microscopic investigation to or- 

 ganic preparations, and after mentioning 

 the assistance derivable from polarised 

 light, describes how inquirers, not pro- 

 vided with special petrol* >gical or polari- 

 sation Microscopes, may yet make suc- 

 cessful use of an ordinary working in- 

 strument. 



Instead of a Bertrand's lens, he in- 

 serts into the long tube an auxiliary 

 Microscope of about 80 mm. focus, in 

 connection with a weak ocular (2 Zeiss) 

 of 30-25 mm. focus, set in the ordinary 

 short draw-out tube. The arrangement 

 is seen in fig. 104 : — P, the polariser ; 

 C, the condenser ; K, the crystal plate ; 

 Ob, the objective system of the Micro- 

 scope ; Ob', the objective system of the 

 auxiliary Microscope ; 0, the ocular ; A, 

 the analyser. 



In order to convert rectilinearly 

 polarised into right-handed circularly 

 polarised light, a quadrant mica slip 

 is introduced between the polariser ami 

 analyser, in such a way that its axial 

 plane makes an angle of 45° with the 

 plane of rotation with the two crossed 

 polarising prisms. The author gives ten 

 figures of the resulta obtained by his 

 apparatus ; they include both uniaxial 

 and biaxial crystals taken in different 

 planes. 



Zeiss' Focussing Microscopes. — In 

 many cases it is found that the ordinary 

 focussing glass fails to satisfy the re- 

 quirements of copying processes. Some- 

 times the magnification is not sufficient, or 



* This subdivision contains (1) Stands; (2) Eye-pieces and Objectives; (3) Illu- 

 minating and other Apparatus; (4) Photomicrography; (5) Microscopical Optics 

 and Manipulation ; (6) Miscellaneous. 



t Zeitschr. wiss. Mikr., 1900, pp. 145-55 (11 figs.). A similar arrangement was 

 described m Journ. R.M.S., 1892, pp. 683-4. 



