ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



491 



constructed as to allow of subsequent additions to the stage and sub-stage 

 equipment. The body is fitted with Berger's micrometer movement, 

 and the draw-tube is at its lower end provided with a slide to admit a 

 mounted Amici-Bertrand lens through an opening in the outer tube. 

 The instrument is furnished with analysers and polariser, with selenite, 

 mica, and Biot-Klein quartz plates — suitable arrangement being made 

 for inserting these plates in a sliding carrier above the objective. The 

 revolving vulcanite stage is graduated at the circumference, and has a 

 line index. The two upper lenses of the swing-out condenser, N. A. 1 ■ 40, 

 are easily detachable, as their mount is not screwed but slipped on over 

 the lowest lens. Additional accessory apparatus can be supplied. 



(2) Eye-pieces and Objectives. 



Zeiss' Compensating Ocular 4* with Iris Diaphragm.* — Messrs. 

 C. Zeiss have modified one of their series of compensating oculars by fit- 

 ting it with a collecting-lens of large diameter (fig. 56). As compared with 

 its predecessor 4, its field is considerably enlarged, 

 though only adapted for use with objectives of 

 16 mm. and 8 mm. The ocular is fitted with a 

 revolving collar, and can be fixed in any desired 

 position by means of the clamping-screw K. An 

 iris diaphragm supersedes the ordinary fixed 

 diaphragm. The eye-lens is mounted in a sliding 

 sleeve, so that a scale can be used if required. 



Fluid Lenses.f — W. A. Bublee, U.S. Consul- 

 General at Vienna, states that a Hungarian chemist 

 has succeeded in producing optical lenses by a 

 simple and cheap process that are not only quite 

 as good as the best massive glass lenses at 

 present used, but that can be manufactured of a 

 size three times as great as the largest homogeneous 

 glass lens heretofore made. Though the invention is more important for 

 astronomical work, lenses of smaller diameter for photographic purposes, 

 for opera glasses, reading glasses, etc., can be produced at correspondingly 

 smaller cost. The lens consists of a fluid substance inclosed between 

 two unusually hard glass surfaces, similar to watch crystals, in w r hich the 

 refractive power and other characteristic properties are so chosen that 

 the glass surfaces not only serve to hold the fluid, but also combine with 

 the fluid to overcome such defects as are scarcely to be avoided in 

 ordinary lenses. It is for this reason that the lens is achromatic. 

 The fluid contained in the lens is hermetically closed in, so that no air 

 can enter and exercise a damaging influence. The fluid does not 

 evaporate, and its composition is such that its properties are not affected 

 by time or temperature. The coefficient of expansion, both of the glass 

 and of the fluid, is approximately the same between the temperatures of 



* Carl Zeiss' Catalogue of Microscopes and Microscopical Accessories, 33rd ed., 

 1906, p. 18 (fig. 5). t English Mechanic, lxxxiii. (1906) p. 473. 



2 K 2 



