Microscope retailer's card (detail)

This photograph shows a detail of the microscope retailer's trade card, which is glued to the inside of the box, under the tray of components. This reveals that, although made by Hugh Powell of London, the microscope was sold by John Cail of Newcastle-upon-Tyne. He was listed at the addresses of 61 Pilgrim Street and 45 Quayside between 1844 and 1855.

In the 17th century it was recognised that the single lens simple microscope gave better microscopic vision than did the compound form, although it was far less convenient to use. Spherical aberration, a fuzziness of the image caused by the spherical curvature of the lens, was especially noticeable. David Brewster (1781-1868) suggested a lens with the sides ground away to form a grooved sphere, and his idea was publicised by Henry Coddington (d. 1845), becoming known as the Coddington lens.

Henry Powell made a few simple microscopes supplied with Coddington lenses, before he joined his brother-in-law, Peter Lealand in partnership in 1841. The instrument derives mechanically from the 18th century acquatic design, sometimes used for looking at pond life.

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