ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



G15 



are designated (55), (a ), (a 2 ), (a 3 ), and (PI), and are respectively of 

 working distances 70, 54, 4(3, 30, 35 mm. The combination (PI) is 

 recommended as a plankton searcher. 



Zeiss' Orthomorphic Eye-piece.*— A Ramsden eye-piece is made by 

 the Jena firm specially for use with Greenough's binocular Microscopes. 

 The name " orthomorphic " is applied to it because of the original 

 design of combining it with small diaphragms in the region of the 

 upper microscopic nodal point in order to satisfy Mr. Greenough's 

 " orthomorphic " requirements. The magnifications obtained by com- 

 binations of this eye-piece and any of the objectives in last paragraph, 

 range between 15 and 72 diameters. 



(3) Illuminating and other Apparatus. 



Zeiss' Centring Apparatus for Microscope Objectives when used 

 as Condensers.f — In many instances it appears desirable to use achro- 

 matic, or apochromatic, objectives as illuminators instead of ordinary 

 condensers. For this purpose a sliding sleeve is supplied with centring 



(mmwmmuuumMmw 



Fifi. 120. 



collar into which such objectives may be screwed, and which fits into 

 the sleeve of the illuminating apparatus. The arrangement is seen in 

 fig. 120, where u u' are the centring screws, and r the screw for clamping 

 the condenser in the sliding sleeve. 



Solar Projection Apparatus and its Adjustment.} — A. H. Cole 

 recommends a solar projection apparatus fitted with a porte-lumiere, 

 instead of a heliostat, as being a cheap, manageable, and effective arrange- 

 ment. A porte-lumiere and a heliostat are both intended for reflecting 

 sunlight : but the porte-lumiere is hand-regulated, whereas the other is 

 clockwork-regulated. The author mounts his apparatus on a wide 

 board of sufficient length to exactly fit into any desired window. The 

 window-sash should be raised, the board then placed in situ, and the 

 sash then drawn down close on to the board. Any supplementary fixing 



* Catalogue, English edition. 1902, pp. 19 and 72. 



t Tom. cit, p. 32 and fig. p. 31. «*-,,« » 



* Journ. Applied Microscopy, v. (1902) pp. 179o-/ (1 ng.). 



