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c. 1848-55

COLLECTION OF: Dr Jurriaan de Groot

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*This is an example of a Lister-limb microscope made by Powell and Lealand, also known as their 'Student' - or 'Iron' - model. The foot and limb are made of black japanned iron. The Lister limb is mounted to one side of a 90 mm high pillar by means of a conical pin, which can be tightened using a short Tommy bar. As a result, the stage and limb are offset relatively to the iron bird-claw foot, which has a spread of 195 mm. There is a sliding rest on the stage which measures 112 x 92 mm, and has a 35 mm diameter central aperture. The only means of illumination is a one-sided concave mirror, which is attached with a gimbal to the tailpiece on a sliding sleeve. The 202 mm long brass body tube slides within a 132 mm long brass outer tube, which is attached to the limb with 4 screws. The single coarse focus knob is placed on the right, and activates a pinion which acts on a rack which is recessed into the body tube itself. There is no fine adjustment on this instrument. The inner tube has a push-fit eye piece diameter of 29.8 mm.

The outer brass tube is engraved 'Powell & Lealand, London'.

Accessories include 2 top hat eye pieces of x5 and x10 magnification, 1 inch and ¼ inch pre-RMS Powell & Lealand objectives, and a glass plate with ledge. A pre-RMS P & L 2 inch objective and objective changer were later added. When in use, the microscope stands 410 mm tall. Its original case measures 215 mm (W) x 190 mm (D) x 390 mm (H).

It remains somewhat uncertain when Hugh Powell made his first Iron model, but E.M. Nelson, in his 1899 paper, considers this may have been about 1838-40, whereas other sources report 1843. The striking resemblance of the coarse focusing mechanism featuring internal rack with an earlier Lister-limb type Ross microscope dated Ca 1835-6 may not be a coincidence. Whereas Ross soon abandoned this focusing arrangement, Powell & Lealand continued to employ it on their Iron model, until the very last one was made in 1911. This kind of focusing arrangement was also found on some microscopes made by J.B. Dancer, as in the Dancer example on this site.

During its long life, the 'Iron' or Student model did come in a number of variations, although the characteristic offset 'bird-claw' foot remained a constant. Examples are known with a white metal outer tube (see Golub No. 279), and a considerable number feature a nose-piece fine adjustment in contravention to Hugh Powell’s opinion that a quality accurate coarse adjustment was always better than a poorly functioning fine adjustment arrangement. Indeed, it was claimed that with the Iron model microscope a ½ inch oil immersion objective could easily be focused using the coarse adjustment alone!

Examples of this microscope are also known with Varley-lever stages acting from below and others acting from above, of the design invented by Alfred White (see the article about Varley's and White's stages). Some examples feature an under-stage condenser with bayonet fitting, as well as a swing-out dark well holder, as also present on Powell & Lealand’s 1843 'New model' microscope, and this arrangement can also be found on Dancer’s microscopes.

With regards to the iron foot, this is japanned black, or sometimes green and occasionally brown. The feet are always plugged with cork. In some models, the foot and limb are carried out entirely in brass, or the foot is cast in bronze. It is obvious that Powell & Lealand were still manufacturing for the trade around this time, as examples are known which carry the name of other retailers, notably Carpenter & Westley.

E.M. Nelson firmly rejects the criticism that more sophisticated Continental microscopes could be purchased for the same money. These were not only smaller, and therefore less convenient in use, but also lacking in stability. He concludes:
'A microscope of this description will be found very useful, not only for rough work, such as examination of unmounted objects, and for roughly searching finished slides, but also for a hack microscope, as a companion to a larger instrument on which critical work is being performed'
. Similar praise is expressed by Professor John Quekett in all editions of his Practical Treatise :
'This microscope is available for all the purposes to which the more costly ones are applied, and is particularly useful to the medical student, to whom its low price is also a great recommendation'.

E.M. Nelson. 'The microscopes of Powell, Ross, and Smith. I. Hugh Powell’s microscopes' J. Roy. Microscopical Soc. 1900, pp 282-97

E.M. Nelson. 'Powell’s Iron microscope'. J. Roy. Micr. Soc. 1899, pp 209-13

J. Quekett. Practical Treatise on the use of the Microscope. 1848. p 82

G. L’E. Turner. Essays on the History of the Microscope. 'Powell & Lealand – Trademark of Perfection.' pp 119-30

*We are grateful to Dr Jurriaan de Groot for providing the images and text about this instrument on our site for everyone to enjoy.