ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 753 



joint. The instrument, which is made by the firm of R. and J. Beck, 

 is used in the vertical position. 



Beck's Parabolic Illuminator. — This apparatus (fig. 174) consists 

 of a mirror made of glass, silvered at the back. The construction was 

 suggested by Mr. Stead as being preferable to a solid silver reflector, 

 which becomes tarnished when used in the presence of chemicals. The 

 apparatus slides on the barrel of the objective, and is thus kept central, 

 and the focusing is effected by moving it up or down. The light should 



Fig. 174. 



be thrown upon it from one side by means of a condensing lens, or 

 otherwise from a lamp on the same level. The light is then converged 

 upon the object in an oblique cone. When in use the lower edge 

 almost touches the object. It is provided with an extra sleeve for fitting 

 it to two object-glasses. It is only suitable for low powers. 



Beck's Parabolic Illuminator with Sorby's Reflector. — This (fig. 

 175) is similar to the preceding, but has the addition of a silver mirror 

 at 45° on a swinging fitting, which can be placed over half the front of 



Fig. 175. 



the object-glass, and throws a direct beam of light upon the object. 

 With this apparatus the effects of oblique and direct light can be rapidly 

 contrasted. It is only suitable for low-power lenses having a long 

 working distanoe. This has both reflectors made of silvered glass as 

 in the preceding illuminator. 



Stbehl, K. — Beleuchtungsprincipien. Central-Zeit. f. Opt. u. Mech- 



(1905) pp. 227-8- 



(4) Photomicrography. 



Vertical and Horizontal Photo-micrographic Camera. — This con- 

 sists of a strong metal base, which carries by means of a hinged bracket 

 a solid circular bar. This rod has sliding upon it two strong brackets, 

 the upper one of which carries a frame with folding ground glass and 

 runners to take a double dark slide for photographic plates 6J in. by 

 4f in. ; the lower bracket carries a tubular sleeve which fits loosely but 

 in a light-tight manner over a tube which may be attached to the eye- 



Dec. 20th, 1905 3 e 



