166 THE HIST"KY AND DEVELOPMENT OF THE MICROSCOPE 



\\v hope ili.-it ii may become the general fine adjustment for this 

 fiirui of microscope in place of the <>1.1 form of direct-acting screw. 



In contract and comparison with Campbell's differential screw 

 we may put tin- principle on which the usual simplified construction 

 of the line adjustment of the Zeiss stands rests. 1 In fig. 127 the 

 triangular liar < ' i- screwed firmly to the stage ; on it moves a hollow 

 piece II. \\hich is connected inseparably with the arm A carrying the 

 tulie. At its uppei- end (_' is cut away for about 15 mm. and B 

 holloued out at a corresponding place so that space is obtained for j\ 

 spiral spring, This spring bears below against the hollowed-out 

 part .if I!, its upper end being connected with the projections of the 

 piece 10 screwed into C. The piece B is closed above by the cap F, in 

 which is the female screw. On the top of the micrometer screw is 

 fitted a bell shaped head, and at its lower end is a small nut for 

 prevent ing over -screwing. The lower end of the screw is rounded off 

 and bears against the flat surface of a hard steel cylinder let into E. 



< 'learly. when worked, the screw remains in the same place. 

 bearing against C. The female screw, on the other hand, moves over 

 it. raising and lowering the tube carrier B A connected with it. By 

 its own weight A B counteracts the rise and thus supplies the place 

 of the strong spiral spring formerly employed. The weak spring 

 here adopted acts in the same direction as the weight of A B, and 

 serves to assist the latter when the upper part of the microscope is 

 placed horizontally. 



Our appreciation of all that is done by the great firm of Zeiss we 

 need not reiterate; it is well known ; but our opinion of the form of 

 stand adopted by these opticians we freely expressed, and we believe 

 justified in the last edition of this book; but it is well to get the 

 opinion of one u ho uith practical knowledge would certainly not be 

 prejudiced against the ('ontinental stand. Dr. H. E. Hildebrand 

 says that in le.-iching establishments, where as many as two 

 hundred microscopes may lie used, the weak points of the Continental 

 stand are soon brought to light. The fine adjustment screw soon 

 becomes unsteady (an ine\ itable consequence of the weight so fine a 

 screw has to carry), the prism suffers bending or rotation, the prism 

 flange or the hinge-block under the object stage loosens its connec- 

 tion with the, stage plate. A'c. A'c.. all of which and much more, as we 

 believe, is the result of the adaptation of a simple and primitive form 

 to complex appliances for which it was never designed or intended. 



It is. however, an admirable characteristic! of the firm of Zeiss, 



lli;it while they adhere doggedly t<> the old ( 'ontinental model, they 



are continuously putting forth their ingenuity and skill to counter- 



\liat are shown to be its defects. In their best usual form the 



"I ...... I <>!' the line adjustment is , ,', , inch for each revolution of the 



This is undoubtedly too rapid, but it could scarcely be 



because, as we have seen, it had the coarse 



and lube to lift, and the wear and tear on so fine 



in constant use led to rapid failure. But the firm has 



luced in 1886, and was it ^-cat improvement on its pre- 



bad. ra< B.M.S.J. 1886, i>. 1051. 

 Mikr. xii. i 1895] ]<]> 1 ' 



