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c. 1830's

Varley VIAL microscope
Varley dark chamber on microscope

vial microscopedark chamberCornelius Varley constructed microscopes from the 1820's through the third quarter of the nineteenth century. As such, most of his microscopes predated the adaptation of the achromatic and adjustable illumination systems. In fact, in the 1820's and 1830's even achromatic objectives were not readily available.

Varley's Dark Chamber is a very simple device. It consists of concentric cylinders, the outermost (C) fitted under the stage. An opening in the top of this part is no more than the aperture of the objective with which it is being used. An inner cylinder (D), slides into this with another but larger aperture in its lower portion; the distance of this second aperture from the top aperture of the device is varied to promote optimal illumination of the specimen without allowing extraneous light to interfere with observation. Because the diameter of the top aperture would have to vary with different power objectives, no single Dark Chamber (unless it had interchangeable upper apertures), could be used with more than one particular objective. The interior parts of these chambers are all colored flat black to prevent reflections.

In the version of the Dark Chamber used with Varley's Vial Microscope, a spring kept the upper end, which was curved to match the shape of the vial, in contact with the vial during use.

The Science Museum in London has five different Varley Microscopes, and although all use compound optical tubes, they are all outfitted with Dark Chamber Illuminators. Three of these have lever controlled movement to the stage.