20 



stage is graduated, is provided with vernier, and has also two rect- 

 angular motions. It can be rotated by hand or clamped, when it is 

 rotated either way by an endless screw working on its circum- 

 ference. The ocular portion is supported by an outer upright, and 

 has its own adjusting screw. The analyser is placed in a slit in 

 the base of the tube, so as always to be in a fixed position when 

 in use, but can be removed by turning about a hinge, but the 

 polariser rotates. The cross lines of the eyepiece are illuminated 

 when the nicols are crossed by a small side mirror, and in 

 the base of the ocular tube a B^rtrand lens is fitted, which can 

 be focussed by means of a screw. Six objectives, one of very 

 long focus, which may be'rapidly attached by a spring ar- 

 rangement are supplied with the instrument. It has also the 

 Bertrand-Lasaulx combination for producing strongly con- 

 vergent light, and the usual quartz wedges, &c. to fit into a slit 

 above the objective. The accessory apparatus consists of two 

 extra eyepieces, three additional lenses, a right angled prism, 

 forceps, six quartz-plates, a stage micrometer, and condensing 

 lens on stand. 



58. Petrographic microscope designed by Prof. C. 

 Klein of Gottingen. 



E. 127. 1886. Made lij Voigt and Hochgesang. 



This stand is on the usual horseshoe base, on a short upright 

 support, about which the upper part turns on a horizontal axis. 

 The stage is graduated to half degrees, and there is a vernier 

 of 30, making the reading to minutes. It is rotated coarsely by 

 hand, or slowly by a tangential screw. The polariser, which is 

 graduated to 5, slides into its carrier and then may be elevated or 

 depressed by a screw. Over the polariser the Bertrand-Lasaulx 

 condensing lenses provided may be fitted also. Diaphragms are 

 provided to fit the same carrier. There are two circular super- 

 stages, with motions in perpendicular directions, effected by 

 means of screws with graduated heads. The surface of the upper 

 one is also graduated in directions parallel to the motions, by 

 which means the position of an object can be recorded. Each turn 

 corresponds to J mm., and the graduation is to 50 parts, so that 

 the arrangement serves as a micrometer reading to -01 mm. 

 The coarse adjustment is by rack and pinion, and the fine by 

 a large screw head working vertically and graduated into 

 250 parts each corresponding to J mm. descent, so that a thickness 

 of -002 mm. may be determined. The objectives are centred by 

 two screws at right angles. The analyser fits over the eyepiece 

 and is graduated to 5 degrees. There is also a second fixed 

 analyser which slides into the tube near the objective. Into the 

 same slot slides a Bertrand lens, and both may be raised or 

 depressed by a screw. Below there is a slit to receive a quartz- 

 plate, quarter-undulation-plate, mica-plate, or selenite-plate, of 

 such a thickness as to give the red of the first order, which are 

 provided. There are six objectives, Nos. 1, 2, 4, 5, 7, and 9 of 



