ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



705 



Fig. 159. 



ture of 0-98, and if the exact thickness of slip for which the condenser 

 is corrected he used, its total aperture is aplanatic. A special feature is 

 that the field-lens is not so limited in size as to interfere with the quick 

 work necessary for histological and diagnostic purposes, as it is -^ in. 

 in diameter. The front lens mount has been so shaped as to obviate, as 

 far as possible, any obstruction of the mechanical stage. The back 

 lens, which does the correcting, is a triple one, and is the system adopted 

 by Messrs. Watson in their series of holoscopic objectives and oil-im- 

 mersion condenser. The carrier is the same as that used for the Abbe 

 illuminator, and will interchange with it. It has iris diaphragm and 

 rotating cell for coloured glasses, black patch stops, &c. 



Seibert's Cylinder Iris Diaphragm. — This (fig. 159) is intended 

 as a substitute for the ordinary diaphragm stop of the Abbe illuminating 

 apparatus, and consists of an iris with domed steel plates. It is fitted 

 in the upper part of the sleeve collar of the condenser system, and 

 during the use of the latter is out 

 of action. When its use is required, 

 the condenser is screwed out, and 

 the iris brought to the desired 

 aperture by pushing a lateral knob. 

 The position of this stop is exactly 

 the same as that of Abbe's dia- 

 phragm, and the plates, when com- 

 pletely closed, touch the object-slide. 



Weinschenk's Guide to the Use 

 of the Polarising Microscope- — 



This book deserves a fuller notice 

 than that given to it in the Biblio- 

 graphical list.* It claims to be a 

 condensed general treatment of the 

 subject. Special commercial and 

 technical applications of polarisation 

 are unnoticed. The main divisions 

 of the book are : — The Polarising 

 Microscope in general ; the adjust- 

 ment of the Polarising Microscope ; observations with ordinary light ; 

 observations with parallel polarised light ; observations with converg- 

 ing polarised light ; twin images and optical anomalies ; Appendix — 

 Auxiliary Apparatus. The chapters are illustrated with a large number 

 of explanatory diagrams. There are also representations of a great 

 many forms of polarising apparatus collected mainly from the catalogues 

 of Nachet, Seibert, Voight and Hochgesang, and Zeiss. 



(4) JPhotomicrography. 



Wandolleck's New Object-holder for Photomicrography. t — The 



intention of this apparatus is to facilitate the photography of solid 

 objects. On a horse-shoe Microscope foot of the usual shape and size 

 (fig. 160) a small vertical pillar carries, by means of a dove-tailed wedge, 



* Cf. this Journal, ante, p. 587. 



t Zeitschr. wiss. Mikr., xviii. (1901) pp. 1-9 (2 figs.). 



