ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 



90Q 



image, that the value of A 0, so obtained, agreed with the value of d 

 calculated from Airy's more complete formula for achromatism, viz. : — 



d 



/A" 1 



-CA+A)(*-*)" ! 



where d = distance between the lenses ; fif 2 , the focal distances of field 

 and eye-lenses respectively ; u, the distance between the field-lens and 

 the centre of the objective. 



(4) Photomicrography. 



New Device for Stereoscopic Photomicrography.*— F. E. Ives has 

 recently made a one-plate-one-exposure stereoscopic photomicrographic 



Fig. 40. 



camera which is interchangeable with his single camera on the adjustable 

 base.t It consists of a light telescopic box camera for plates 8-J- by 6 in., 

 provided at the front with a small prism-box containing three equilateral 

 prisms so disposed as to divide the light at the eye-point above the eye- 

 piece of the Microscope, and project the divided rays upwards to form 

 the two stereoscopic images. Fig. 40 shows the parts drawn to scale. 



* Jonrn. Franklin Institute, cliv. (1902) pp. 391-3 (2 figs.). 

 ,t Op. cit., cliii. (1902) p. 375; and this Journal, 1902, p. 491. 



