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C. 1880 and 1847

Author: Barry Sobel

Editor: Joseph Zeligs

The Powell and Lealand microscope polarizer and selenites with condenser on Ross Microscope

In order to satisfy the demand for P & L accesories that fit microscopes by other makers, P & L supplied these larger versions of the Powell & Lealand-type of large substage polarizer and set of swing-out selenites. Both the polarizer and selenite stack have fitting tubes of about 2 inches outer diameter. The polarizer fits into the bottom of the Ross substage 2 inch sleeve, while the stack of selenites fits into the top. The selenite stack includes 3 selenites, each of which can be swung out of the optical axis and individually rotated by their knurled disks. The selenites in this example came with a signed Powell & Lealand Apochromatic Condenser, adapted to the larger diameter threads on top of the selenite fitting.

This shows the polarizer installed on the bottom of the 2 inch substage sleeve of a circa 1847 Ross Barlimb microsope, and the selenite stack and condenser installed on top to the 2 inch substage sleeve. This older model of Ross microscope does not provide rotation of the substage, but the polarizer allows manual rotation of the central part containing the prism, which is attached to the knurled disk at the bottom.

The top of the selenite fitting has a blackened brass disk screwed on to it and has a threaded opening with an inner thread diameter about 0.86 inches (22 mm). A signed Powell & Lealand condenser requires two adapters to fit the top of the selenite housing. The female threads of the condenser (13 mm inner diameter), fit onto the male threads (13.1 mm diameter)on the top of the first adapter. The bottom of that adapter has male threads (outer diameter of 17mm), which fit into the female threads on top of a second adapter (16.7 mm outer diameter). The second adapter has bottom male threads (22 mm diameter), which fit into the threaded disk on top the the selenite housing (inner diameter of 21.7 mm). The adapters with this selenite housing were obviously designed to accomodate a variety of different condensers, but none of these adapters would accept an RMS threaded objective or condenser.


This set of polarizer and selenites have a significantly larger diameter than the standard versions that fits the Powell and Lealand No 1. Unlike the standard fittings, where the selenite has a larger fitting than the polarizer, the barrels of the selenite and polarizer fittings that fit the Ross substage of the 1847 Model are both the same diameter(2 inches or about 51 mm). One should note however that although the barrels are of bigger diameter, the housings of the selenites are exactly the same diameter, though the thread for the condenser on top is of larger diameter on the bigger version. Therefore the smaller threaded opening on the standard selenite fitting accepts the male threaded P & L condensers or the female threaded one with only a single female to male adapter. Although in the smaller version each selenite has inscriptions indicating the primary axis and retardation, in the case of the larger one, no such marks are found, though the overall construction of the device, including the selenite discs, is nearly identical. The reader will also note that the selenite disks are mounted exactly the same way in both devices but inverted so that the disks that they are screwed to are on top of each fin on the standard version and on the bottom of the fins of the larger version.