ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 257 



heads acting on the surface and entirely within the circumference.* 

 It is mounted on the Zentmayer system, and graduated near the edge, 

 " finders " being engraved in convenient positions ; two centering 

 screws are provided by which exact rotation round the optic axis can 

 be secured ; and it can be easily removed, or may be replaced by a 

 glass or metal friction-stage, &c. A simple and effective plan has 

 been adopted of applying the iris-diaphragm, hemispherical im- 

 mersion illuminator, or Wenham's " half-disk " illuminator, beneath 

 the stage, where they are held by a small projecting peg and a spring 

 latchet. 



The substage can be removed entirely from the lower part of the 

 limb by means of a metal dove-tail slide The usual rectangular 

 (centering) and rotating motions are provided. 



The substage condenser is furnished with a centering cap and a 

 rotating plate of the usual series of slots, central stops, &c., an iris- 

 diaphragm immediately beneath modifies the diameter of the circular 

 opening utilized. 



The coarse adjustment is of the usual " Jackson " form by means 

 of a spiral pinion and diagonal rack-work. 



The fine adjustment acts directly upon a vertical slide carrying 

 the objective only, and is controlled by vertical milled heads on both 

 sides of the nose-piece. 



In illustration of the variety of motions obtained with this Micro- 

 scope, Fig. 36 shows the sector inclined at about the usual position 

 for working with central illumination ; Fig. 37 shows the lateral 

 inclination of the limb, &c., the sector being at its highest position ; 

 Fig. 38 shows the Zentmayer swinging tail-piece clamped to the 

 sector (as suggested by Mr. J. Mayall, jun.), the limb being inclined 

 laterally, and the substage removed. This lateral inclination of the 

 limb causes the stage to revolve upon a central horizontal axis, so 

 as to present the object to the illuminating pencil at all obliquities ; 

 Fig. 39 shows the sector at the lowest point so that the microscope- 

 body is horizontal, the tail-piece being clamped to the sector, the 

 limb swung laterally about 45° (to the right), and the substage re- 

 moved. This position of the sector would be that required for 

 measuring angles of aperture by means of the graduations on the 

 circular base. The axis of the lateral inclining motion is also 

 graduated, so that either the degree of inclination of the limb or 

 that of the swinging tail-piece can be registered. In all these posi- 

 tions, and indeed in every position in which the various movements 

 enable it to be placed, the Microscope is very steady. 



The construction of the stand has been carried out by Messrs. 

 Ross under Mr. Wenham's instructions, and we understand that they 

 purpose making such modifications as will permit a lamp to be 

 carried by the swinging tail-piece, or placed at the lower end of the 

 sector ; and the mirror to be attached at pleasure to a rotating slide in 

 the centre of the base : these additions will add still more to the 

 facilities for obtaining obliquely incident light. 



* See the descriptions of similar stages, this Journal, i. (1881) pp. 116-117 

 (Figs. 9 a.nd 10), p. 300 (Fig. 46), and pp. 944-6 (Figs. 221-3). 



Ser. 2.— Vol. II. S 



