ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



761 



analyser is a slit for the selenite and quartz plates. The objective is. 

 centred on the rotation centre of the rotatory object-stage, by means of 

 two centring screws acting on a centring nose-piece. 



Leitz' Handloups.* — The catalogue numbers of these are 69 and 70. 

 The loups (figs. 165, 166) consist of two achromatic double lenses, pro- 

 ducing a field very large, flat and free from tint. The magnifying powers 

 are five and eight-fold, the corresponding diameters of the lenses being 31 > 

 and 2P. mm., while the field of view measures 35 and 20 mm. respectively.. 



1 mm 



T 'MlBW. l i,iaj 



1 



Fig. 165. 



Fig. ICG. 



Very Powerful Micrometric Microscope.f — P. Boley finds that the 

 " double Microscope," which he designed J for observing the slightest dis- 

 placement of the mercurial meniscus of the capillary electrometer, can 

 be also used for ordinary purposes as a micrometric Microscope. In 

 principle the Microscope is one in which the ordinary ocular is replaced 

 by a true compound Microscope of large objective. It is formed of a 

 tube double the usual length, with the principal objective at the anterior 

 end, the objective of the ocular Microscope in the centre, and the actual 

 ocular at the posterior end. The ocular-holder is tube-shaped and slides 

 inside the main tube. The whole is fitted on a stand having three 

 rectangular movements for controlling the field. The image obtained 

 is erect, and the original magnification is increased from four to six- 

 fold. 



Watson's "Argus" Attachable Mechanical Stage. — This is a 

 simplified form of mechanical stage, which can be readily attached by 

 a single thumb-screw (fig. 167). The moving plates are not fitted in dove- 

 tailed grooves in the ordinary manner, but slide on guides, and are held 

 in position and actuated by a frictional wheel made of brass and covered 

 with indiarubber. This wheel is revolved by means of a milled head, 

 which can be set in any position from the horizontal to the vertical, 

 the movement taking place at right angles to its own direction. 



The horizontal and vertical positions are indicated by spring catches, 

 but between the two points a range of diagonal traverse is given when 



♦ Catalogue, No. 40, Nov. 1902, p. 64. 



f Trav. Sci. Univ. Renno.-!, i (1902) pp. 310-2. 



X Tom. cit., p. 277. 



