108 



THE MICROSCOPE. 



The stao^e is circular in form, with concentric rota- 

 tion, horizontal and vertical mechanical movements, 

 and top slide for holding the objects, trough, etc., while 

 under examination. It has a clear aperture underneath 

 of 3 in. when the apparatus plate is removed, and, in 

 consequence of the improved plan of mounting the 

 mirrors from the back, a great obliquity of illumination 

 can be obtained as well as a considerable range of 

 movement when a sub- stage is fitted. 



Collins's Dissecting Microscope, for plant or insect 

 dissection (fig. 61), has a firm metal stand, sliding 



adjustment for focuss- 

 ing, two simple lenses, 

 to be used together or 

 separate, with mirror 

 for illuminating. 



Swift's Challenge 

 Microscope (fig. 62), 

 of the Jackson- Lister 

 form, which experi- 

 enced microscopists still 

 believe, for many rea- 

 sons, to be one of the 

 best, is well finished in 



'Microscope, on ^^ ^^ fa Q coarge . 



adjustment is sensi- 

 tive; the focussing can be accurately done by it 

 alone, whilst the fine-adjustment is so conveniently 

 placed as to be within easy reach of one of the fingers 

 of the hand which works the rack. By a somewhat 

 novel arrangement, Messrs. Swift have succeeded in 

 mounting the analyzer above the Weiiham's prism 

 within the binocular body, so that it can be easily 

 brought into use by pushing it into the optic axis of 

 the instrument, without any screwing or unscrewing 

 of the objective. To those in the habit of frequently 

 employing the polariscope, this simple arrangement 

 must commend itself, as the definition of the object- 

 glass is much less interfered with by this method of 

 mounting the analyzer than where the Wenharn prism 

 intervenes between it and the eye-piece. The instru 



FIG. 61. Collins's Diasecti 

 Prof. Henslow's 



