198 SUMMARY OF CURRENT RESEARCHES RELATING TO 



MICROSCOPY. 

 A. Instruments. Accessories, etc.* 



1) Stands. 



Fuess' New Petrographic Microscope for the Theodolite Method.! 



E. von Fedorow's discovery that the principle of the theodolite could be 

 advantageously applied to crystallographic and petrographic instruments, 

 has resulted in a somewhat extensive use of the method. C. Leiss now 

 describes its application to tlie above Microscope (fig. 11), which em- 

 bodies certain improvements which have been suggested by Nikitin and 

 Wright. 



The stage is constructed for the reception of object-glasses 28 by 

 48 mm. In this instrument it is not necessary to use thin sections 

 uncovered and with the polished face upwards, but the preparation is 

 placed in the ordinary way on the stage and kept steady with spring- 

 clamps. The stand is non-inclinable and is strongly built. The upright 

 arm t supports the (so-called immobile) axis of the vertically divided 

 circle /, rotatory by means of the spoke-wheel r, and capable of being 

 clamped by a screw (not shown in the figure). Firmly connected with / 

 is the projecting piece Z, for carrying the combined circular systems, 

 viz. the circle //, the auxiliary circle ///, and the two removable divided 

 arcs IV. The circle //has a (so-called mobile) rotation axis in I and is 

 clamped by the screw s. The rotation or inclination of the auxiliary 

 circle ///, which carries the preparation, takes place with reference to 

 the sockets zz \ zz cannot be clamped. In order that the polished 

 face of the preparation lying on /// can be brought accurately into the 

 prolonged imaginary axis of circles / and ///, the position-plate (which 

 is independent of the circle ///) for receiving the preparation can be 

 screwed up and down within necessary limits ; the nut which governs this 

 movement is therefore in circle ///. All three circles and the two arcs are 

 divided into degrees. Yerniers reading to 5' are fitted to the two main 

 circles / and // ; in the other cases the reading is taken by a pointer. 

 The usual rotation of the whole Microscope about a vertical diameter is, 

 in this instrument, replaced by a more convenient arrangement for the 

 rotation of the two nicols (polarizer P, analyzer A). The rotation- value 

 is given by the circle N, graduated to degrees, and two verniers reading 

 to 5', the combined nicol-rotation being effected by the rod n. For 

 certain purposes the analysing prism A can be rotated alone, the rotation 

 being read off on the small half -circle A^. In such a case the rod n is 

 separated from the connecting-arm a, in order that the tube may be 



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

 Illuminating and other Apparatus ; (4) Photomicrography ; (5) Microscopical 

 Optics and Manipulation ; (6) Miscellaneous. 



t Zeitschr. f. Instrumentenk., xxxii. (1912) pp. 377-9 (1 fig.). 



