ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



283 



For the 75 mm. objective a specially small lens of great focal length 

 is used as condenser, since it is here necessary to project an image of 

 the source of light within the objective. The condenser for use with 

 the electric arc light consists of two plano-convex and one concavo- 

 convex lens L (fig. 49). The part of the system near the lamp is fixed 



Fig. 49. 



once for all at the proper distance for producing a parallel beam, and 

 to diminish spherical aberration the concave face is turned to the lamp. 

 The part turned to the Microscope, which brings the parallel rays again 

 to a focus, is movable in a sliding socket which permits the displace- 

 ment of the image on the optic axis within pretty wide limits. 



Detmeks, H. J. — Photography with High-powers by Lamp-light. 



Proc. Amer. Soc. Micr., X. (1888) pp. 143-8 (1 fig.). 

 F. C. S. — Beginner's Guide to Photography. 



[Includes 'Apparatus for Pbotomicrograpliy,' pp. 58-62.] 



128 pp., 34 figs., 8vo, Loudon, n.d. 

 Gray, W. M. — Photomicrography. 



Queen's Micr. Bull., V. (1888) pp. 21-2, from ' Science of Photography.' 

 Neuhatjss, E. — Anleitung fiir Herstellung von Mikrophotogrammen. (Guide to 

 preparing Photomicrographs.) Aerztl. Centr.-Anzeig., 1888, No. 38. 



Perken, Son, and Eayment's Photomicrographic Apparatus. 



E7igl. Mech., XLVIII. (1889) pp. 369-70 (1 fig.). 

 Swift and Sons' (J.) Photomicrographic Apparatus. 



[Lord Edward Churchill's. See this Journal, 1888, p. 1061.] 



Scientific News, II. (1888) p. 379 (1 fig.). 



C5) Microscopical Optics and Manipulation. 



Microscopical Optics. — Eecent occurrences would appear to show that 

 we have allowed too long a period as the measure of a microscopical 

 "generation." In ordinary life thirty years is considered to represent a 

 generation, and as it is less than ten years since the more salient facts of 



u 2 



