Goniometers are instruments for measuring the interfacial angles of crystals. While crystals might look different, those of the same substances were found to have the same interfacial angles, and measurement of these angles could thus be used to determine the composition of the crystal.

The angles can be measured by passing a beam of light through a telescope and detecting the reflected beam in another telescope, both telescopes being mounted on a divided circle with the crystal in the centre. This type of goniometer looks rather like a spectroscope.

English chemist, William Hyde Wollaston (1766-1828) invented a goniometer in 1809 which used the reflection of light off the faces of a crystal. This was mounted on the axis of a divided circle, and the observer adjusted the crystal until a ray of light was reflected from one crystal surface. The crystal was then rotated until a second surface reflected the ray of light in the same direction. The angle between the faces could be determined by the difference between the readings on the divided circle.

004  Crystal Goniometer   1853-1863 R. 1043  Signed: Elliott Brothers, 30 Strand Foot span 181; Height 296; divided circle height 247; diameter 161. Brass, A tripod foot, with 3 levelling screws, holds a vertical pillar leading to the centre of a 6-spoke divided circle (10-360degrees). Revolving in the centre of the circle is a disc mirror, whose housing is attached to an arm ending in a window with a vernier to read the scale.
005  Crystal Goniometer   c1880 G. 1041  Signed: Yeates & Son Dublin Foot span 163; height of scale table 195; diameter of scale 148. A red painted iron tripod foot supports a conical brass pillar, leading to a brass disc, with an angled ivory divided edge (0-350degrees). On top of this is an oxidised brass disc to hold the crystal, with a pointer to read the scale.
006 Crystal Goniometer 1876-1913R 1044  Signed: R. Fuess Berlin Marked: Geol. Dept. U/C/D Dublin. 4 Foot span 232; height 268; divided circle housing height 154; diameter 151. Brass and white-metal. 3 curved legs have brass levelling screws.
007 Wollaston Crystal Goniometer 1864-1886R 1047  Signed: Spencer & Son 19 Grafton Strt Dublin. Marked: Geol. Dept. U.C.D. Base diameter 150; height 171; disc diameter 122. Brass and oxidised brass. A mahogany base holds a trunnion support to the axis of a disc, divided on its edge (0-180) and (10-170).
008 Wollaston Crystal Goniometer 1843-1858G 1048  Signed: Yeates, 2, Grafton Strt Dublin. Marked: Geol. Dept. U.C.D. Base 118x113x15; height 162; disc diameter 12. Brass. A mahogany base holds a trunnion support to the axis of a disc, divided on its edge (0-180) and (10-170).
009 Wollaston Crystal Goniometer Mid to late 19c. 1046  Signed: Yeates & Son, Dublin. Marked: Geol. Dept. U.C.D. Base 129x127x25; height 145; disc diameter 112. Brass. A mahogany base holds a turned pillar with a cube on top.

Chemistry Page

Spectroscopy