24 Modern Microscopy 



bearing more tightly, and so takes up any wear caused by 

 friction. Any microscopist can therebj' adjust his own 

 instrument. 



This pattern of fine adjustment in modified forms is 

 now made by at least two other houses. It would not be 

 applicable to microscopes other than those in which the 

 so-called Jackson limb is employed, and makers of stands 

 in which a direct acting screw is fitted, as in the Continental 

 form, have exercised considerable ingenuity in providing an 

 efficient movement. Carl Eeichert, of Vienna, who has in 

 recent years shown highly progressive tendencies, designed 

 a lever- form of fine adjustment for this latter description of 

 microscope, which has proved even more satisfactory than 

 was originally anticipated. Messrs. Swift and Son, too, 

 have adopted a somewhat similar plan with corresponding 

 success, while Messrs. Zeiss have devised an entirely distinct 

 fine adjustment for their photographic stand, actuated by 

 means of gear-wheels, which produce an extremely slow 

 and precise movement. 



Powell and Lealand's instruments are also provided with 

 a fine adjustment having special merit, consisting of a lever 

 actuating a long tube sliding up and down inside the body. 

 This, however, has the disadvantage of being carried by the 

 rack-work when focusing for different powers. 



Tvpo-speed Fine Adjustments. — Complaint has arisen 

 that the tendency to fit very slow-acting fine adjustments 

 has become a source of inconvenience to students and others 

 who work interchangeably with objectives of different powers 

 fitted on revolving nose-pieces. To meet this Mr. A. Ashe, 

 of the Quekett Club, designed a two-speed fine adjustment, 

 and the plan was carried to a practical issue by Messrs. E. 

 and J. Beck, who now apply it to certain of their instru- 

 ments. It is shown fitted to the microscope (illustrated 

 page 25). It will be noticed that two milled heads are 

 provided for fine focusing instead of the usual one. The 

 upper milled head turns a screw having a coarse thread, 

 moving the body -g\ inch for each revolution; the lower 



