apparatus for measuring angle of incidence
Date: circa 1765
Inventory Number: 0087
Classification: Angle-Measuring Instrument
Subject:
Attributed to: Benjamin Martin (1704 - 1782)
Cultural Region:
Place of Origin:
Dimensions:
53 x 21.5 x 19.7 cm (20 7/8 x 8 7/16 x 7 3/4 in.)
graduated circle diam.: 21.5 cm (8 7/16 in.)
Bibliography:
The Apparatus of Science at Harvard, 1765-1800
Description:
This instrument is made of a brass circle with scale marked every half degree and numbered every ten degrees. Each quadrant is numbered twice from 0 to 90° and from 90° to 0. A rectangular mirror is fixed to the horizontal diameter. Two rotating radial arms end in sight vanes and verniers. The circle stands on a tapered octogonal shaft and a round base. The latter is adjusted with four leveling screws.
In Collection(s)
Signedunsigned
FunctionThis instrument was used to measure the angles at which light was either reflected from surfaces or refracted through various materials. It demonstrated, in other words, Snell's law.
Historical AttributesThis instrument most likely came from the shop of Benjamin Martin. His invoice dated from September 1765 and sent to Harvard includes "A Compleat Apparatus for ye Angle of Incedence by refraction & Reflection".
Curatorial RemarksSome accessories such as prisms and containers of liquids, which would have accompanied the original instrument, are now missing.
Primary SourcesBenjamin Martin, The Philosophical Grammar; Being a View of the Present State of Experimented Physiology, or Natural Philosophy, 2nd ed. (London, 1738).
Published ReferencesDavid P. Wheatland, The Apparatus of Science at Harvard, 1765-1800 (Cambridge: Harvard University Press, 1968), 121.