ZOOLOGY AND KOTANV, Al JCUOSCOPV, ETC. 



97 



adjustment gives a free working distance between the nose-piece and the 

 stage of of in. The fittings of the substage apparatus and also the 

 eye-pieces and objectives are of the R.M.S. standard size. The mechanical 

 stage is constructed as part of the instrument, but by an ingenious 

 arrangement can be removed and a plain metal plate substituted. 



The compound substage has centring screws so that the condenser 

 may be rendered axial with any objective ; it is fitted with rackwork 

 to focus, and can be turned aside out of the optical axis when desired. 



The fine-adjustment (fig. 17) is of the vertical lever pattern. A is 

 the actuating milled liead turning the screw B, on which is fixed a 



Fio. 17. 



rounded nut : this presses against the lever C. The fulcrum is at D, 

 and the sliding fitting is raised by pressing against tlie disk E. The 

 reactionary effect is produced by the weight of the body and its fittings 

 and the coil spring F. The long lever and the short distance between 

 the fulcrum an'd the point of pressure produce a slow and sensitive move- 

 ment. The milled head A occupies a fixed position and does not travel 

 with this screw. The rate of movement of the adjustment is read on 

 the divided drum G : a complete rotation of the milled head moves the 

 body • 1 mm. 



Microscope Stands (English v. Continental). — Two articles on 

 this subject have lately appeared in Nature." They contrast the English 



* Nature, No. 2199 (Dec 21, 1911) ; No. 2202 (Jan. 11, 1912). 

 Feb, 21st, 1912 H 



