100 SUMMARY OF CURRENT RESEARCHES RELATING TO 



for polarisation. The analyser is screwed into the bottom of the draw- 

 tube, in which position it does not limit the field of view as when 

 mounted in the eye-piece, and must 

 lie capable of independent rota- 

 tion. 



Leiss, C. — TJeber eine Verbesserung an 



der Polarisationseinrichtung von Mi- 



kroskopen. 



[The essential part of the arrange- 

 ment consists in the facility for 

 moving aside the polariser, 

 which is fitted in a sleeve on 

 a hinged arm, the illuminating 

 and condenser lenses being un- 

 affected. The low-power con- 

 denser lens is independent of 

 the polariser, and the latter is 

 proti eted l<y a cover-glass.] 



Tachermak's Mineral, u. Petrog. Mitth., 

 XXI. (1902) p. 454. 



Leiss, C. — Krystallpolymeter nach C. i2"-l-:'J 



Klein. 



[The author gives a full descrip- Fig. 25. 



tion of the instrument.] 



Zeit.f. Instrumentenk., XXII. (1902) p. 201. 



Wendt, G. von. — Eine ausgezeichnete Beleuchtungsquelle fur mikroskopische 

 Zwecke. 



[Strongly recommends the use of the Nernst lamp for microscopy. The 

 light is constant, and when used with strong magnifications (2000 or 

 more) the whole of the field is extraordinarily bright. The author con- 

 siders it superior to any artificial or even natural light-source.] 



Zeit.f. wiss. Mikr., XVIII. (May 1902) pp. 417-8. 



(4) Photomicrography. 



Stereoscopic Photography of Microscopic Objects.* — W. Scheffer, 

 after explaining the optical principles underlying the subject, proceeds 

 to their application. When the object to be photographed has been 

 brought into the field of view, the ocular is then removed, and one 

 notes the position of the light-source (i.e. the carbon filaments of the 

 lamp described in a previous section, fig. 18 supra). As the direction of 

 the lateral displacement marks the horizontal, it is best to arrange that 

 this displacement should be parallel to the edge of a plane. This is most 

 conveniently attained by setting the lamp, with its stand, in such a 

 position that the direction of the arm should be perpendicular to the 

 longer edge of the plane, and this can be judged very accurately by the 

 eye. By means of the screw a lateral movement in one direction is now 

 given to the lamp until the carbon filament lies close to the periphery 

 of the field ; then it is similarly moved to the opposite side. "When the 

 observer has convinced himself of the accuracy of these positions, the 

 ocular is re-inserted, the object laid on the stage, and the first photo- 

 graphic plate taken. The carbon filament is then moved to the opposite 

 position and the second plate taken. Stereograms so obtained were 

 compared with the object, and were found to give an excellent physical 

 presentation, exactly corresponding to reality. The camera used was 



* Zeitschr. f. wiss. Mikr., xviii. (190J) pp. 408-12 (2 figs.). 



