220 THE AMERICAN MONTHLY [September, 



The fine adjustment is the improved form. One revolution 

 of the milled-head moves the body i -300th of an inch, and as it 

 is sensitive to the i-iooth of a turn, a motion of 1-30000 part of 

 an inch can be obtained. The body carries the Continental size 

 eye-pieces and with draw-tube closed is of Continental length. 

 The draw-tube, which is graduated to centimeters, when out to 

 its full extent makes the length of the body 10 inches. The in- 

 side diameter of the top of the draw tube is smaller than the re- 

 mainder, the former making a fitting for the eye-piece about i 

 inch long, permitting of the tube being blacked inside up to this 

 fitting, and so minimizing reflection. The lower end of the draw- 

 tube is provided with a screw of the universal size, so that the 

 lowest powers may be used. The stage is of extra large size, 

 being 3^ inches square, so allowing of the use of large slips, etc. 

 It is mounted at a convenient height for support to be given to 

 the hands, when manipulating the object, and, being below the 

 centre of the inclining joint at the top of the foot, a perfect bal- 

 ance of the parts is obtained. The fitting for under-stage appa- 

 ratus is hung on a pivot, allowing of it and the apparatus 

 contained in it to be at once turned aside (leaving the mirror free 

 for use) and replaced as required. The mirrors are plane and 

 concave, and are mounted on a swinging arm, permitting of their 

 being swung aside for photography, also allowing of light being 

 thrown on the object very obliquely. They are also adjustable 

 to focus by means of a sliding fitting. The fittings are all of 

 universal size. The eye-pieces have nickle-plated tubes to pre- 

 vent tarnishing. All the movements are fitted with screws, 

 which, by being very slightly turned, compensate for wear and 

 tear caused by friction. 



This instrument is also made in the binocular form, or if made 

 to order the body can be furnished of any desired large size. In 

 short, the instrument is complete, with every mechanical conven- 

 ience, as supplied to leading microscopists, professors, etc., 

 throughout the world. (See frontispiece.) 



MICROSCOPICAL NEWS. 



The microscopic determination of rock-forming min- 

 erals. — A book, in Russian, bv F. Loewinson-Lessing. bearing 

 this title has been published in St. Petersburg. It contains tables 

 of the rock-forming minerals based on the writings of Rosenbusch, 

 Michel Levy, and Lacroix as well as of Doelter and Hussak. If 

 you know the characters of the mineral, the book enables you to 

 determine its name. One table is based on examination with 

 polarized light. Others depend on external morphological char- 

 acters, the crystalline systems and other optical characters. About 

 So of the most practically important minerals are included and all 

 others are excluded. 



