106 SUMMARY OF CUEEENT EESEAECHES. 



MICROSCOPY. 



A. Instruments, Accessories, &c* 

 CI) Stands. 



Cbamot's Microscope for Microchemical Analysis-! — This instru- 

 ment, which is made by Messrs. Bausch and Lomb, has been designed 

 by the inventor to meet the growing demands of microcbemistry. The 

 Microscope is intended to be efficient, cbeap, and suitable for class work, 

 and its general nature is that of a simplified petrographic instrument. 



Tbe stand (fig. 1) is of tbe Continental type, and, since its use would 

 always be vertical, it was not thought necessary to provide it with a 

 jointed pillar. The coarse adjustment is by rack-and-pinion, and the 

 fine by micrometer-screw. The stage is circular, rotating, provided with 

 centering-screw ; its circumference is graduated into degrees for measur- 

 ing crystal angles. The stage is faced with rubber, and the substage is 

 adjustable by means of a quick-acting screw. Into the substage is fitted 

 the polarising apparatus, consisting of a Nicol prism of large size, and so 

 mounted that, by means of a pin fitting into a slot in the substage-ring, 

 the prism can always be replaced in exactly the same position. The 

 polariser can be swung aside when polarised light is not desired. The 

 prism is so arranged that it can be rotated, and is provided with a circle 

 graduated in degrees. The analysing nicol is also provided with a 

 graduated circle, and it is so mounted that it fits over and above any 

 eye-piece. The draw-tube of the Microscope is furnished with a small 

 projecting pin, which fits into a slot cut in the bottom of the tube- 

 mounting of the analyser. This slot lies in the same vertical plane as 

 the zero points of the analyser, the polariser, and the stage. The zero 

 points of polariser and of analyser are arranged as usual, i.e. for the 

 position of crossed nicols. It follows, therefore, that when the polariser 

 is at zero, and is swung in position below the stage, and the analyser is 

 also at zero, and is in position with its slot on the pin, the nicols are 

 crossed without further adjustment. It is therefore possible to quickly 

 change eye-pieces, drop the analyser in place, and not be obliged to 

 spend time in adjusting it, as is so often the case. Magnifying power is 

 obtained by low objectives and high eye-pieces, so as to diminish risk to 

 the objectives from corrosive fluids. Each eye-piece is provided with 

 cross-hairs at right angles, and a projecting stud fitting into a nick in 

 the upper edge of the draw-tube for lining them. It is found that 1-in., 

 1/2-in., and 1/4-in. objectives form a convenient set, with 2-in., 1^-in., 

 1-in., and 1/2-in. eye-pieces. This gives a range of magnification 

 between 20 and 500 diameters, which is amply sufficient for all ordinary 

 analytical work. 



The draw-tube of the Microscope is graduated as usual ; the mirrors, 

 plane and concave, are on a swinging bar. 



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

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

 and Manipulation ; (6) Miscellaneous. 



f Journ. App. Micr., 1899, pp. 502-5 (1 fig.). 



