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James Swift and Son, 81, Tottenham Court Road, London, W.

Paragon Microscope.

This is a large binocular microscope, with complete mechanical adjustments. As the usual form of knuckle axis-joint is not used, the centre of gravity does not change when the instrument is swung from the vertical to the horizontal position. The graduation of the circular stage is carried to 5', while the cross movements of its mechanical adjustments are divided to read to 0’01 in. (0'25 mm.). The fine adjustment is graduated to read to 0’0001 in. (0'0025 mm.), and is operated by two milled heads, one on either side of the limb. The Centering Substage is actuated by a rack and pinion motion, and carries an achromatic condenser, N.A. l'0, iris diaphragm, polariser, mica undulation film, and a red and a blue selenite in rotating geared cells. All these accessories may be used separately, or together, or can be swung out of the optic axis. An analyser is mounted in the body of the microscope, immediately above the binocular prism, and works with the polariser.

Dick Mineralogical Microscopes.

This type of mineralogical microscope differs from all other patterns in having a fixed stage and simultaneously rotating prisms, so that, instead of turning the object between stationary prisms, the polariser, analyser and ocular are made to revolve together about the optic axis. By this arrangement the spider lines in the ocular turn on the object which remains stationary, so that the most minute specimen is maintained in position through an entire revolution. Thus the necessity of delicate centering adjustments, to secure absolute concentricity of rotation, is altogether obviated. Both polariser and analyser rotate independently in their divided fittings, and click when they are crossed. A divided circle revolves with the prisms to indicate the angle of rotation. Two focussing Bertrand lenses are fitted through the optical tube, while dustproof slots are provided for the reception of compensators. The various models exhibited differ chiefly in the arrangement of the substage convergent systems.

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