122 SUMMARY OF CURRENT RESEARCHES RELATING TO 



MICEOSCOPY. 

 a. Instruments, Accessories, &c.* 



Bulloch's Lithological Microscope. — The general construction of 

 this instrument (fig. 5), is similar to the Professional stand of Mr. 

 W. H. Bulloch except in the following details : — 



There are two stages, each is graduated to 15' reading by a ver- 

 nier to 20", and can either be revolved by hand or by tangent screw 

 which also acts as a slow motion. The worm cut on the periphery 

 of the stage has 360 teeth (equal to single degrees), and the tangent 

 screw head is graduated to 6°, so that each division reads to 1'. The 

 tangent screw can be thrown in or out of connection as required. 

 Each stage has stops for Maltwood finder, and also stops for the small 

 lithological slides. The above arrangement is common to both stages. 

 One of the stages has a plain sliding object-carrier. The second is 

 also furnished with a sliding object-carrier, and with micrometer 

 screws in two directions "for the direct measurement of objects 

 without any reference to magnification." The screw threads are 

 0-5 mm., the heads being graduated to 250, so that each division 

 reads to 2 /x, and by vernier to tenths equal to • 2 /a. 



At the side of the limb there is a scale reading to • 5 mm., and 

 the slow motion screw-head is graduated to 500, each division equal- 

 ling 1 /x. The polarizing prism fitting in the substage has a graduated 

 circle, and a spring catch at each 90°. The analysing prism at the 

 lower end of the body- tube has a revolving movement by a lever 

 of 90° and can be removed to the side by a slide similar to the 

 Wenham binocular prism. At the lower end of the tube is a Klein's 

 quartz-plate, and a centering nose-piece. A goniometer eye-piece 

 is used with crossed spider lines, a Nicol prism, and a calc-spar 

 plate. The fitting is made adjustable, for if the calc-spar is not cut 

 in the proper direction the cross cannot be placed in the centre of 

 the field without slightly tilting the crystal. 



In working ; to change from polarized to ordinary illumination, 

 the prism below the stage can be turned aside, leaving the wide 

 angle condenser in position ; or the whole substage can be turned 

 aside, a movement which is supplementary to swinging on the axis in 

 the centre with the object on the stage. When the condenser is not 

 required there is a supplementary substage for the lower prism, so 

 that the prism can be used close to the object, and no light admitted, 

 except that which has passed through the prism. 



Chevalier's Portable Microscope. — An ingenious method of pro- 

 viding a solid and steady base for a portable Microscope was devised 

 by M. 0. Chevalier, and is shown in figs. 6 and 7. 



The tripod feet of the instrument fit into three notches in the 



* This subdivision is arranged in the following order : — (1) Stands ; (2) Eye- 

 pieces and Objectives ; (3) Illuminating Apparatus ; (4) Other Accessories ; 

 (5) Photo-micrography ; (6) Manipulation ; (7) Microscopical Optics, Books, 

 and Miscellaneous matters. 



