506 



MICROSCOPY. 



the last few years have brought forth, a large 

 proportion are either imitations or revivals 

 of earlier and abandoned forms the improve- 

 ments made in their details, or the demands of 

 the times, rendering serviceable now the models 

 which were before rejected and forgotten. 



The more or less real requirement of the 

 times has led to the introduction, especially in 

 Germany, of a class of trichina-microscopes, 

 adapted for making a rapid search over a large 

 field with a low power. The flesh to be exam- 

 ined is compressed between large, thick glass 

 plates, which are so arranged as to be carried 

 systematically beneath the lenses by a sliding or 

 rotary motion the whole device being either 

 a portion of a special stand for the purpose, or 

 else attachable to the stage of any stand. A 

 very simple but serviceable " trichinoscope " 

 is made in this country (" J. R. M. S.," 1880, 

 p. 711 ; 1882, p. 258). Such arrangements are 

 also useful when large quantities of vegetable 

 or animal fibers, or hairs, commercial products, 

 etc., are to be surveyed. 



Under the demands of the practically new 

 science of micropetrography, a class of litho- 

 logical, petrological, or mineralogical micro- 

 scopes has been suddenly developed, charac- 

 terized by the completeness of the stage and 

 polariscope arrangements. The stage, often 

 mechanical, has a graduated rotation, a cen- 

 tering adjustment,* and in some cases an at- 

 tachment with graduated arc, after Hartnack's 

 model, for rotating the object vertically under 

 the lenses for the sake of determining the sepa- 

 ration of the optic axes of biaxial crystals, or 

 for the measurements of angles by successively 

 leveling, in the focus of the objective, the cor- 

 responding sides of the crystals. This rotation 

 takes place in Mr. Bertrand's stand, in a glass- 

 bottomed trough upon the stage, so that the 

 measurements can be made in oil or other 

 liquids as well as in air (" J. R. M. S.," 1883, 

 p. 413). The fine adjustment is graduated 

 and indexed for approximate measurements 

 of thicknesses. The polarizing prism is large, 

 mounted with centering adjustment and grad- 

 uated rotation with spring-catch to indicate 

 when the prisms are crossed, with fittings to 

 carry above it a condensing lens of large aper- 

 ture (another lens being screwed at the same 

 time into the lower end of the draw-tube), and 

 with a swinging movement by which it can 

 be instantly turned into or out of the axis of 

 vision. The analyzer has a graduated rotation, 

 and is mounted over the ocular, or in a sliding 

 box above the objective, or both. The ocular 

 has a centering adjustment, a pair of cross- 

 wires (illuminated from the side for use with 

 a dark field) in the focus of the eye-lens, a 

 graduated circle for goniometry, and an ar- 

 rangement for placing a plate of calc-spar be- 

 tween the analyzer and the eye-lens, or in the 



* Sometimes a centering nose-piece is substituted for this ; 

 while, in M. Nachefs model, the stage and body are made to 

 revolve together under the ocular, so that the centering is 

 not disturbed by the rotation. 



focus of the latter, for stauposcopic measure- 

 ments. In or near the nose-piece is a slit, or 

 sliding box, or cranked arm, for introducing 

 a Klein's quartz-plate into the field. No one 

 stand, however, is known to include all the 

 above-named features. Among those promi- 

 nent in the introduction of such special stands 

 may be mentioned Profs. Lasaulx and Rosen- 

 busch, and Messrs. Fuess, Nachet, Sidle (of the 

 "Acme" stands), Bulloch, Beck, Swift, and 

 Zeiss (see "J. R. M. S.," 1882, p. 842). 



The utility of the binocular microscope, which 

 was strenuously denied by some not many years 

 ago, can no longer be reasonably questioned. It 

 is evidently most useful in general natural his- 

 tory, with low powers or moderate angles, and 

 of less advantage, though not absolutely inap- 

 plicable, to investigations requiring only high 

 powers or extreme angles. For small stands 

 of the Continental type the Nachet form was 

 first really successful, and is still preferred; 

 while the Wenham form, which set the exam- 

 ple of a direct transmission of light to one 

 eye and a diverted transmission to the other, 

 continues to be the standard binocular of Eng- 

 lish and American stands. ' One of its few se- 

 rious disadvantages is the small size of prism 

 heretofore admissible, and the accompanying 

 limitation of the acting aperture of many object- 

 ives by the small opening possible in the prism- 

 box of a nose-piece. This has been lately rem- 



Fio. 13. BAUSCH AND LOMB ARRANGEMENT OF WENHAM 

 BINOCULAR. 



edied by the contrivance of Edward Bausch, 

 who abandoned the sliding prism-box altogeth- 

 er, and mounted a larger prism, , in Fig. 13, 

 on a swinging arm, 5, inside of a nose-piece 

 of sufficient capacity to allow it to be swung 

 wholly out of the way, as shown by the dotted 

 lines, leaving unobstructed the whole caliber of 

 the " Society " screw, d. The prism-holder, &, 

 is attached to a steel spindle, c, which is turned 

 by a milled head outside. (This arrangement is 

 shown in situ in the cut of "arc" stand, Fig. 12.) 

 Of the many ingenious binoculars proposed 



