Beck Cheshire's apertometer
Date: circa 1907
Inventory Number: 1122d
Classification: Microscope Accessories
Dimensions:microscope: 44 × 25 × 24 cm (17 5/16 × 9 13/16 × 9 7/16 in.)
case: 15.9 × 47 × 24.2 cm (6 1/4 × 18 1/2 × 9 1/2 in.)
Accessories: eyepiece telescope to magnify image
DescriptionThis is a Beck "Small Best" convertible binocular-monocular compound microscope with a full complement of accessories. Due to the complexity, the objects have been divided into the following:
1122a: Beck convertible binocular-monocular microscope
1122b: Beck case with objectives, oculars, and common accessories
1122c: Beck patent revolving substage condenser
1122d: Beck Cheshire's apertometer
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The Cheshire's apertometer (1122d) consists of a series of semicircular concentric arcs ranging in size from smallest on the inside to largest at the outside. The arcs are numbered from the center 1-9 and then 0-5. The label reads "CHESHIRE'S APERTOMETER." They are printed on white paper housed underneath a thick disk of clear glass. The glass is held in a brass cylindricaL box with a screw-top lid.
A special eyepiece telescope could be used to magnify the image on the back of the objective. It looks very much like the erecting glass used with objectives found in the case of accessories (1122b).
Signedon box lid: R & J. BECK. LTD.
FunctionTo test objectives in order to determine their numerical aperture (N.A.). The number of rings seen in the back lens of the objective gives the aperture in decimals, each ring being 0.1 N.A.
Historical AttributesThis Wenham-type binocular microscope by R. & J. Beck was Alexander Agassiz's personal instrument. It was used at his Marine Biological Laboratory in Newport, Rhode Island, where Agassiz summered. The instrument appears with Agassiz in a portrait that shows him working in this lab. Corrosion on parts of the microscope are probably due to contact with marine creatures and sea water.
This microscope was given to the Ernst-Lewis Collection on May 18, 1936 by Dr. Thomas Barbour, Director of the Museum of Comparative Zoology.
According to the correspondence between Conrad Beck, managing director of R. & J. Beck, and Dr. Frederic T. Lewis in 1939, the microscope is the type called the "Small Best" and was made in 1876. With all the accessories, it would have cost between £60 and £80.
Primary SourcesR. & J. Beck, Catalogue of Microscopical Apparatus (London, 1907), p. 6.
"Illuminating and other Apparatus: Cheshire's Apertometer," Journal of the Royal Microscopical Society, 1907, p. 736.
ProvenanceAlexander Agassiz, Marine Biological Laboratory, Newport, Rhode Island, c. 1876; Museum of Comparative Zoology, Harvard University, c. 1910; transfer by Thomas Barbour, MCZ Director to the Ernst-Lewis Collection of Microscopes (inv. no. 122), Harvard Medical School, May 18, 1936.