MODEL: SWIFT 'SYMPOSIUM' WALE-LIMB 'RESEARCH' MICROSCOPE

DESCRIPTION: This microscope, unfortunately no longer in my collection, is a Wale Limb Polarizing Microscope. It has a smoothly operating Wale limb inclination joint with clamp. There is diagonal rack and pinion coarse focus, side fine adjustment, and diagonal rack and pinion adjustment to the outer draw tube. A second draw tube pulls out. Both draw tubes are graduated. There are separate controls for the X and Y axis of the mechanical stage each with scales. The mechanical stage rotates and can be locked in position. There is a Bertrand lens in the lower part of the optical tube. The substage has condenser fittings above a polarizer. There are dovetail condenser mounts for quick exchange of condensers.

HISTORY OF THE SWIFT 'WALES LIMB' MICROSCOPES.

This may be one of the last of the Wale Limb microscopes. It was sold to me at auction from Bonhams in 1999 as lot 109 and was previously exhibited with the Arthur Frank Loan Collection in Glasgow 1973. Unfortunately it is no longer in my own collection. In 1920, a symposium* was held in London during which Powell Swift described a research microscope which he had jointly developed with R & J Beck, in consultation with two of the most respected names in microscopy at the time, Sir Herbert Jackson and Mr J. E. Barnard. The instrument combined several previously well-known features into a stand felt to represent an instrument optimized for any type of research at the time. That microscope featured a Wale limb and several additional features.

It featured a Wale Limb, (invented by the American George Wale) which Swift had provided on prior instruments for many years. The Wale limb had been developed to avoid shifting the center of gravity during inclination, but Swift pointed out that this version, avoiding an axle through the limb, would allow inclination so smoothly that adjustments such as the focus, would not be disturbed in the slightest way during inclination.

Second, it featured a rack and pinion drawtube, and a supplementary drawtube, inside the first, allowing the tube length to be adjusted from 140 to 250 mm.

Third, it featured the Beck double-lever fine adjustment, providing the ability to focus on even the finest details at high powers with ease.

In addition, its stage was said to be unusually rigid and supported through a right angle cradle said to be superior to most arrangements of the time. The stage had a 2 3/4 inch travel, thus allowing metallurigical use. The stage also had concentric rotation, as well as the X and Y motion. It was also provided with the ability to be centered in the optical axis.

A unique feature was the use of the Sloan objective changer in the substage, allowing rapid changing of substage accessories. The same type of changer was said to be supplied to the nose, but in the example shown here, a triple objective changer is found instead, and the Bertrand lens is integrated into the tube above the objectives. The nosepiece Sloan objective changer was originally said to accept multiple accessories including a Bertrand lens arrangement, a waveplate, or a vertical illuminator.

Another feature was the massive 'A-frame' foot which could be bolted to the table for photomicrography. All the rack and pinions were of the spiral or diagonal type, invented by Swift.

For further discussion of the history of the Wale limb microscopes, and in particular the Swift Wale limbs, see the Swift Wales Limb main page.

*Spiers, FS, Editor: The Microscope, its Design, Construction and Application A Symposium and General Discussion By Many Authorities Charles Griffin & Company Ltd London 1920.