484 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



r the arithmetical mean of the radii r^^ r^ of the inner and outer edges of 

 the circular holder.) In such cases a closer value of R is got from 



R 



h 



ih 



-'- + ;; + < 



(1) 



R is first approximately calculated from the formula by omitting e, that 

 is from 



R = "l^ll + ^' 

 ih 2 



The value of R, so obtained, is then substituted in — 



Sh 



Then the value of e is substituted in (1), and the final value of R so 

 obtained. The revised formula gives a result differing by 1*5 p.c. from 

 that obtained from the ordinary formula. 



Leitz iPhotographic Objectives with Iris Diaphragm.* — These 

 new formula objectives (fig. 71)) were designed for the Edinger, the 



Fig. 79. 



photomicrographic and projection apparatus of 64, 42, 35, and 24 mm. 

 focal distance, and have proved useful for a number of purposes. 



Hall, J. J. — The Magnifying Power of Eye-pieces. 



English Mechanic, Ixxxv. (1907) Nos. 2200-2. 



(31 Illuminating- and other Apparatus. 



Demonstrating the Pseudo-vacuoles of Yeast-Cells.f — J. J. van 

 Hest, after referring to the difficulty of illuminating yeast-cells and 

 bacteria by any other than transparent light, describes how a kind of 

 incident illumination can be attained by a process of lateral action. 

 Under ordinary circumstances parallel light impinging on the mirror is 

 reflected upwards through the condenser, and the rays cross before 

 entering the objective. The object is therefore illuminated on all sides 



* E. Leitz' Catalogue, No. 41. English edition, 1905, p. 11. 

 t Centralbl. Bakt. Parasitenk'., xvii. (1906) pp. 94-5. 



