ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



731 



Beck's London Microscope : Iris Model.* — In this new model 

 (fig. 115) of the London Microscope f there are the following improve- 

 ments and additions : a clasp handle for the inclining joint ; more 

 room between the stage and the base ; an iris diaphragm to the stage ; 

 and an arrangement whereby the substage can be swung aside, so that 

 the condenser can be instantly displaced from the optic axis by means of 

 the same milled head which actuates the focusing adjustment. As soon 

 as the condenser has been racked down to its lowest limit, it swings clear 

 of the stage. 



(2) Eye-pieces and Objectives. 



Koristka's jV Oil-immersion Objective.^ — The focal length of this 

 has been reduced to 1 • 8o mm., and thus a higher magnification is 

 obtained. The objective is adapted for the most diverse purposes. 

 While the instrument is equal in effect to a ^i^ inch, the old denomina- 

 tion has, for simplicity, been retained. It is made with N.A. of 1"30 

 or 1-37. 



Koristka's New Objective 6*. — This, numbered as above,§ has a 

 focal length of -t-Smm. and X.A. 0*82. It reseml>les No. G in the 

 same maker's series, which has the same focal length, but N.A. 0'72. 

 Its frontal distance is • 50 mm., and both act as objectives of strong 

 penetration, being very useful in such matters as the computation of the 

 red and white blood corpuscles. The new objective, however, acts 

 better in those researches in which a higher power of resolution is 

 required, e.g. the cases of diatoms. 



Voigtlander and Sons' Objectives. |1 — The 

 construction of the apochromats is shown in 

 fig. lie. They are absolutely free from cbro- 

 matical aberration ; hence their applicability to 

 microphotographic work and the finest and most 

 difficult examinations. Among their new lenses 

 of this class are those of focal lengths, 12 mm., 

 6 ■ 5 mm., and 3 • 7 mm. ; with respective N.A. • 5, 

 0-75, 0-95. 



The achromatic objectives of the dry systems 

 have low optical indices, the highest being that of 

 16 mm. focal length and "28 N.A. 



The firm have brought out a new water im- 

 mersion achromat of 5 mm. focal le.ngth and 

 N.A. 0'75 ; and a new oil-immersion of 2*7 mm. 

 and N.A. 0*35. 



Fig. 116. 



Voigtlander and Sons' Eye-pieces. *![ — These include four Huyghenian 

 eye-pieces of magnifications 5*5, 7 • 5, 9 • 2, 11*4 ; and five compensating 

 eye-pieces of powers G"2, 8*3, 11' 4, IG'7, 25 '0. 



* R. and J. Beck's Special Catalogue, 1907. 



t See this Journal, 1901, pp. 694-5, fig. 145. 



X Supplement to General Catalogue, N 12, Milan, April, 1907. § Loo. cit. 



II Catalogue (English edition) 1907, p. 7. t Tom. cit., p. 11. 



