ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 459 



adjustment is by diagonal rack-and-pinion ; the fine by a delicate 

 micrometer screw with graduated head. The draw-tube is nickelled and 

 graduated, and the body-tube into which it fits is felt-lined. 



Three methods of illumination are used : — (1) A large thin glass 

 vertical illuminator, fitting into the top of the draw-tube, as shown in 

 fig. 95. (2) The thin glass vertical illuminator of English form, used 

 just above the objective ; and (3) a Zeiss vertical illuminating prism 

 used in same position as (2). Each of these has its special advantages, 

 and all are generally supplied with the instrument. 



The stage is double. A large mechanical stage, with ample move- 

 ments in both directions, has attached to it, by means of levelling screws, 

 an upper plate without central opening. On this is placed the metal to 

 be examined. 



The compound stage, as thus constructed, is attached to the main 

 post of the Microscope by a strong sleeve with separate rack movement. 

 This permits the object to be brought into focus without disturbing 

 either the optical part of the instrument or the position of the light. 

 This is a very important feature. The entire stand revolves upon the 

 base, and the stage may also be swung out separately if desired. 



The outfit includes two eye-pieces, three objectives with revolving 

 triple dust-proof nose-piece, and stand complete ; in a polished mahogany 

 case, with lock. 



Giinther's New Loup Stand.* — C. Benda describes this stand, consist- 

 ing of a metal pillar of 32 cm. in length, standing on a solid fairly 

 heavy metal plate (20x13 cm.). On this moves a rotatory sleeve, 

 pushable up and down, and clamped by screws. The sleeve is firmly 

 connected with a horizontal arm of about 40 cm. in length, so that this 

 is movable in all directions about the vertical pillar. The arm consists 

 of two limbs, approximately equal in length, and connected by a hinge- 

 joint, movable in the horizontal plane. The distal limb is hollow, and 

 receives the loup-stalk 20 cm. long. This stalk can be drawn out, re- 

 versed, and clamped by screws. The loup can thus be set and secured 

 in any position. The loup supplied has a diameter of 9 cm., and a focus 

 of 10 cm. 



Special Stand and Specimen-holder for the Microscopical Examina- 

 tion of Metals. — For the microscopical examination of metals vertically 

 reflected light must be used, — that is, light reflected downward by means 

 of a vertical illuminator placed between the nose-piece of the Microscope 

 and the objective. The source of light, condensing lenses, &c, must be 

 so arranged that the beam of light will enter the vertical illuminator. 

 With the ordinary stand any change of objective, or a change in the 

 thickness of the piece under examination, necessitates a corresponding 

 lowering or raising of the tube and, therefore, of the vertical illuminator 

 attached to it. The beam of light then no longer enters the illuminator 

 as it should, and the source of light and other illuminating appliances 

 must be raised or lowered. To obviate this troublesome manipulation, 

 the stand (fig. 96) used in the Boston Testing Laboratory, Boston, 

 U.S.A., is provided with a stage capable of up and down motion by rack- 



* Arch. f. Anat. u. Phye., 1900, pp. 179-80 ; and Zeitschr. f. wiss. Mikr., 1900, 

 pp. 199-200. 



