758 SUMMARY OF CURRENT RESEARCHES RELATING TO 



MICROSCOPY. 



A. Instruments, Accessories, &c." 

 (1) Stands. 



Leitz' Mineralogical Stand, No. Lj— This stand is numbered 37 

 in the makers' series, and is shown in fig. 163. In its general dimen- 

 sions it corresponds to the Leitz stand known as No. 1 A. The coarse 

 adjustment is by rack-and-pinion, and the fine by a micrometer screw 

 graduated into fifty divisions, a graduation signifying a movement of 

 O'Ol mm. The condenser, iris diaphragm and polariser are raised and 

 lowered by rack-and-pinion. Observation of the axial images is con- 

 veniently performed by means of a three-limbed condenser, which can, 

 by means of lateral pxish-movement of the stop-carrier under the stage, 

 be drawn out and replaced. The objective is centred on the rotation- 

 centre of the rotatory object-stage, by means of a centring nose-piece. 

 The stage itself is graduated into 360° with a vernier ; it also bears 

 graduations for orientating. The Nicol acting as a polariser can, after 

 removal of the iris diaphragm from underneath, be itself drawn out. 

 The 0°, 90°, 180°, 270° of this Nicol are marked. The analyser is set 

 in a metal holder in a fixed position over the ocular, and the rim of the 

 indicator is graduated into 360°. On the front of the tube is a flap 

 which can be opened and closed, and through which the inner tube is 

 accessible ; in the inner tube there is a slit for the reception of a 

 Bertram! lens. The function of this lens is to assist the ocular in 

 magnifying the interference figures formed in the converging polarised 

 light ; lens and ocular are raised and lowered together, as desired, by 

 means of rack-and-pinion. In the analyser there is a slit (45° to the 

 zero) for films of selenite and Iceland spar. In many investigations it 

 is recommended that, instead of the above, an analyser should be used 

 inserted laterally into the tube. There is a revolver for three ob- 

 jectives. 



Leitz' Mineralogical Stand, No. Il.f — The series-number of this 

 instrument is 39 (fig. 164). The tube is carried by a brass_ foot and 

 pillar, highly lacquered, and the adjustment is by rack-and-pinion. The 

 rotatory stage is graduated on its circumference to 360°, and the reading 

 is by a pointer. The polariser is set in a spring collar, whose zero and 

 quadrant points are marked. The collar with the polariser is inserted 

 in a holder which, by means of a lateral screw, can be raised and lowered 

 or drawn aside. An illuminating lens is placed over the polariser in the 

 stage, and by means of a lever can be turned out of the path of the 



* This subdivision contains (1) Siands; (2) Eye-pieces and Objectives; (3) Illu- 

 minating and other Apparatus; (4) Photomicrography; (5) Microscopical Optics- 

 and Manipulation: (G) Miscellaneous. 



t Catalogue, No. 40, Nov. 1902, pp. 55-7. % Tom - cit -> PP- 58 ~ 9 - 



