800 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the disk of light. The tube into which the convergent lenses, polari- 

 scope, and spot-lens fit, is cut open for the purpose of easily dropping 

 these pieces into position ; this opening is covered with a revolving 

 segment of tube similar to the breech action of the Martini rifle. 



The stage has rectangular motions by cams which are moved by 

 the milled heads at the back of the stage, and the clip holding the 

 object will equally clamp the thinnest slide or a thick zoophyte 

 trough, the clip is lifted by turning the milled head. The coarse 

 focusing is by rack and pinion, and the fine adjustment is similar in 

 construction to that of the ordinary Hartnack Microscope. The alum 

 trough for stopping the heat-rays can be used behind the condensers 

 for convergent rays, or inserted in the opening in front when parallel 

 light is required, the opening being covered by a revolving segment 

 of tube when not used. 



Nelson's Hydrostatic Fine Adjustment.* — E. M. Nelson con- 

 siders that " the growing increase in the use of wide-angled object- 

 glasses calls for an improvement in the fine adjustments of Micro- 

 scopes. This is especially the case when it is remembered that depth 

 of focus is inversely proportional to N.A. Also the Microscope is 

 used in a far more scientific manner than the rough and ready way 

 of former days. Among the best workers critical pictures are now 

 the only ones accepted. A vast improvement has taken place in the 

 construction of object-glasses, but the fine adjustments are pretty 

 much the same as they were twenty-five years ago. The following 

 diagrams illustrate a method that has occurred to me, and which, if 

 adopted, would, I think, effect an improvement in this direction. It 

 is simply an iron chamber filled with mercury, with a plunger and a 

 ram. The fine adjustment screw works on the plunger, and the ram 

 on a stud fixed to the nose-piece, which is kept pressed against it by 

 a spring. Fig. 130 shows the arrangement as adapted to a bar move- 

 ment. Here there are two chambers connected by a pipe, the 



H" 



^ 



Fig. 130. 



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plunger being in one, the ram in the other. Fig. 131 shows the 

 same thing adapted to a Jackson-Lister. It will be observed that the 

 fine adjustment screw may be on either side or behind the bar. 

 Fig. 132 shows it as arranged for the Continental or medical student's 

 model, which has the direct-acting, non-geared-down, screw fine 

 adjustment. The application of this contrivance to these Microscopes 

 would be invaluable, as their present fine adjustments preclude the 

 possibility of any fine work being done with them. As drawn, the 



* Paper read at Quek. Micr. Club. Cf. Engl. Mech., xxxix, (1884) p. 576 

 (3 figs.). 



