670 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Fig. 116. 



The handle M, by which the instrument is held when passed 

 round a class, is hollow, so that it can be placed on a vertical support, 

 if desired. C is a metal cone polished inside, and we gather that at 



P is the arrangement for fine 

 focussing after the tube has 

 been adjusted as nearly as 

 possible and locked. 



Grundlach's College Micro- 

 scope. — This Microscope, till 

 now called the "Physician's 

 Microscope No. 1," is shown 

 in Fig. 117. Its speciality 

 consists in the adjustments, of 

 which there are four, thus 

 described (from the maker's 

 catalogue) : — 



" (1) A rack-and-pinion 

 movement; (2) a sliding ad- 

 justment of the body ; (3) a 

 micrometer-screw, and (4) a 

 combination of micrometer- 

 screws giving a slower motion 

 than has ever been brought 

 into use before. The racks 

 and pinions are cut with some 

 new and original tools and 

 with the greatest exactness. 

 " Gundlach was the first 

 to think of the advantages of the combination of the sliding adjust- 

 ment with the rack and pinion, and to bring out a series of Micro- 

 scopes on this plan. The former allows the body to be removed for 

 changing objectives ; and, by combining the two, the body may be 

 made to stand so high that first-class low-power objectives may be 

 used on these stands. Lower powers may be used on them than most 

 large stands will allow. 



" The ordinary fine adjustment is by micrometer-screw acting on 

 Gundlach's new frictionless roller motion, patented in 1879. This 

 motion is free from the fault of displacement of the optical axis, from 

 so-called loss of motion, and from lateral motion, while it has twice 



the old extent of motion 



" In working high powers, microscopists have felt the need in some 

 work of a slower motion than that of the ordinary micrometer-screw, 

 which cannot be made much finer and still be durable enough. This 

 need is now supplied by the combination of two screws which give a 

 resultant motion equal to the difference in the threads employed. One 

 of these screws is a little coarser than the ordinary micrometer-screw, 

 and may be used alone as a fine adjustment, and a change can be 

 made instantly from this to the finer motion. Either motion is given 

 by one milled head next to the top of the pillar, and the change is 

 made by turning a smaller clamping screw having its head over the 



