two-circle contact goniometer
Datecirca 1896
Inventory Number1997-1-1739
ClassificationGoniometer
Subject
Maker
Peter Stoe
User
Charles Palache
?
1869 - 1954
Cultural Region
Place of Origin
Place of Use
Dimensions17.5 × 17.7 × 12 cm (6 7/8 × 6 15/16 × 4 3/4 in.)
Material
Accessoriesquartz crystal (mounted on wax)
DescriptionThe instrument consists of a circular horizontal disk and a vertical hoop mounted on a tripod. The horizontal disk is divided into 360 degrees and it can rotate around its axis together with the sample holder that is placed in the center. The vertical circle is fixed, but has a mobile radial rod attached to it terminating in a perpendicular contact-plane. The rod can be also moved along the diameter.
The instrument still holds a large quartz crystal attached to it with wax.
The instrument still holds a large quartz crystal attached to it with wax.
SignedPunched on horizontal circle: P. STOE / HEIDELBERG
Curatorial RemarksPossibly, the first two-circle optical goniometer brought to the US; this instrument was acquired by Charles Palache for Harvard University in 1896 (see Clifford Frondel, "An Overview of Crystallography in North America" in McLachlan, Dan and Jenny P. Glusker eds. <i> Crystallography in North America</i> (American Crystallographic Association: New York, 1983), p. 8)
FunctionThe purpose of crystallographic goniometry is to measure the interfacial angles of crystals to determine their type. Single-circle measurement methods determine directly the angle between two crystal faces. In the two-circle method, however, two angles are measured representing the so-called "position angles" from which the relative angle between the faces can be then computed. The "position angles" can be visualized as the intersection points between an imaginary sphere surrounding the crystal and the perpendicular lines to the surfaces of the crystal that pass through the center of the sphere. Each of these points is fully determined by two coordinates, a vertical and an azimuthal angle. The interfacial angles can be then computed using spherical trigonometry. With a two-circle goniometer, under favorable conditions, all faces of a crystal can be measured with a single mounting.
In using the instrument, the crystal is placed on a holder in the center of the horizontal disk. Then, the rod and the horizontal disk are appropriately rotated until the "contact-plane" (i.e. the end of the rod) is nearly in contact and truly parallel to a face of the crystal. The two angles measured on the horizontal and vertical scales represent the coordinates of this surface. This measurement is repeated for the other surfaces.
In using the instrument, the crystal is placed on a holder in the center of the horizontal disk. Then, the rod and the horizontal disk are appropriately rotated until the "contact-plane" (i.e. the end of the rod) is nearly in contact and truly parallel to a face of the crystal. The two angles measured on the horizontal and vertical scales represent the coordinates of this surface. This measurement is repeated for the other surfaces.
Historical AttributesTwo-circle contact goniometer was first described by Victor Mordecai Goldschmidt (1853-1933) in 1896 and first built in collaboration with the mechanic Peter Stoe (see U. Burchard, "History and Development of the Crystallographic Goniometer" (<i>The Mineralogical Record </i>, Nov/Dec1998, 29, 517-583), p. 561).
Johann August Oertling
Date: circa 1860
Accessories: box of crystal holders (2007b)
Object number: 2007a
Stoe & Cie
Date: 1909-1920
Accessories: table-mounted; embedded, modern electric lights
Object number: 2004-1-0338
Rudolf Fuess
Date: circa 1900
Accessories: wooden case; xeroxed article from Crystallography, N. Story-Maskelyne, Oxford 1898, p. 394-399, [The morphology of crystals] (describes in detail the use of the instrument); Stereo photograph of some experimental arrangement, perhaps a spectrometer; Spectrum photograph of Fluorit, signed "Victor Schumann, Leipzig 1901"
Object number: 1997-1-1752
Johann August Oertling
Date: circa 1860
Object number: 2002
Rudolf Fuess
Date: circa 1900
Object number: 1997-1-1731
W. & S. Jones
Date: circa 1797
Accessories: original case
Object number: 1999-1-0034
Rudolf Fuess
Date: circa 1875
Accessories: case
Object number: 1997-1-1740
