Arm protractor and goniometer
Date: dated 1923
Inventory Number: 1997-1-1749
Classification: Goniometer
Subject:
Maker: Samuel Lewis Penfield (1856 - 1906)
Owner: Clifford Frondel ? (1907 - 2002)
User: Department of Geology and Geography, Harvard University ? (1890 - 1961)
User: Mineralogical Museum, Harvard University ? (founded circa 1775)
Cultural Region:
Place of Origin:
City of Use:
Dimensions:
goniometer at 0: 0.3 × 16.3 × 8.3 cm (1/8 × 6 7/16 × 3 1/4 in.)
in envelope: 0.4 × 17.4 × 9.3 cm (3/16 × 6 7/8 × 3 11/16 in.)
Accessories: envelope case
Description:
The instrument consists of a graduated semicircle printed on a card, in combination with an arm of transparent celluloid, swiveled by means of an eyelet at the center of the semicircle. The angle is indicated by an index-line scratched on the celluloid arm. The lower part of the arm was blackened because of the difficulty in bringing a transparent edge in contact with a crystal face. A decimal scale in centimeters is printed on the upper edge of the card, while the circle is graduated with two supplementary angles; inside the circle there is also a scale in inches, and a rhombic grid inside a square (probably used for a more accurate measurement of the subdivisions).
The instrument has also a printed ruler in inches in the middle, below the rhombic grid.
The the ruler and the card are enclosed in a envelope.
The instrument has also a printed ruler in inches in the middle, below the rhombic grid.
The the ruler and the card are enclosed in a envelope.
Signedprinted inside degree circle: ENGINE DIVIDED / ARM PROTRACTOR AND GONIOMETER / Pat. July 31, 1900 / Designed by S. L. Penfield. / Made in New Haven, Conn., U.S.A.
Inscribedon protecting case: ARM PROTRACTOR AND GONIOMETER;
handwritten on the back: CLIFF FRONDEL / 9/17/23 / 94
handwritten on the back: CLIFF FRONDEL / 9/17/23 / 94
FunctionThe purpose of crystallographic goniometry is to measure the interfacial angles of crystals to determine their type.
To determine the angle between two surfaces, one has to hold the crystal edge at the scissor opening between the card and the limb. The angle being measured is read from the scale. Such contact goniometers usually have an accuracy between 15 minutes and 1 degree, and are considerably less precise when measuring small crystals.
To determine the angle between two surfaces, one has to hold the crystal edge at the scissor opening between the card and the limb. The angle being measured is read from the scale. Such contact goniometers usually have an accuracy between 15 minutes and 1 degree, and are considerably less precise when measuring small crystals.
Historical AttributesCardboard contact goniometer in universal use by students in laboratory courses.
Curatorial RemarksMay have been used for instruction and later kept by Prof. Clifford Frondel.
Primary SourcesThe instruction leaflet of a similar contact goniometer designed by Penfield is available here ).
ProvenanceProf. Clifford Frondel, Geology, Harvard University
