ZOOLOGY AND BOTANY, MICROSCOTY, ETC. 



81 



MICROSCOPY. 

 A. Instruments. Accessories, &c* 

 CI) Stands. 



Le Chatelier's Microscope for Examination of Opaque Bodies.f— 

 The inverted position of the stage in this Microscope facilitates the 

 arrangement of fragments of metal, which may then, with the excep- 

 tion of the polished surface, be of any shape. The horizontal pencil 

 of light received by the illuminating prism D (fig. 1) is refracted up- 

 ward and taken up by that half of the objective which is covered by J). 

 The two faces of the prism make an angle of 45°, one of them forming 



Fig. 1. 



an angle of 22*5° with a horizontal line, the other a similar angle with 

 a vertical line, which causes the axis of the reflected pencil to be vertical. 

 The extreme edge of the prism intersects the axis of the objective and 

 also its principal focus, or, at least, comes as near doing so as possible. 

 The diaphragm E, placed at the conjugate focus of the object examined, 

 and the screen F with its rectangular opening, provide a means for 

 cutting off all the useless rays, whose diffusion by the lenses of the 

 objective would otherwise illuminate the field of the Microscope and 

 diminish the visibility of the images. To reach this result, the dia- 

 phragm E must have an opening exactly equal to the diameter of the 



* This subdivision contains (1) Stands; (2) Eye-pieces and Objectives; (3) Illu- 

 minating and other Apparatus; (4) Photomicrography; (5) Microscopical Optics 

 and Manipulation ; (6) Miscellaneous. 



t Metallographist, Jan. 1898, pp. 83-4 (1 fig.). 



Feb. 20th, 1901 G 



