goniometer
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What is a goniometer?
A goniometer is an instrument for measuring angles. A contact goniometer has two metal rules pivoted at the center of a graduated semicircle. The instrument is placed perpendicular to the edge between two crystal faces, and the rules contact the faces to measure the angle between them. Reflecting goniometers are more precise, using reflected images of a bright object from crystal faces to measure angles accurately. Some advanced goniometers have multiple circles for complex measurements without readjusting the crystal.
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What does a goniometer measure?
A goniometer is an instrument for measuring angles. Reflecting goniometers are high-precision instruments that measure angles on small crystals with smooth faces. The crystal is turned, and the angle is determined by a graduated circle to which the crystal is fixed.
Horizontal-circle goniometers require the crystal to be mounted and readjusted to measure each set of faces. Two-circle goniometers overcome these issues, and three-circle goniometers add another graduated circle, allowing measurements in any zone without readjusting the crystal.
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How is a basic goniometer used?
A basic goniometer is an instrument for measuring angles. A contact goniometer consists of two metal rules pivoted at the center of a graduated semicircle. To measure a crystal, position the goniometer so it is perpendicular to the edge between two faces of the crystal. Bring the two metal rules into contact with the crystal faces. The angle between the rules, which you can read on the graduated semicircle, indicates the angle between the two faces. The rules are often slotted, so they can be shortened when measuring crystals that are partly embedded.
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Where might you find goniometers being used?
A goniometer is a device used to measure angles between crystal faces. There are different kinds of goniometers, and they can be found in slightly different contexts.
A contact goniometer can be used for the approximate measurement of large crystals. A reflecting goniometer is an instrument of greater precision used for the accurate measurement of angles when small crystals with smooth faces are available. Mineralogists use reflecting goniometers to help determine a mineral's crystal system.
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How does a goniometer help measure angles in human joints?
A goniometer is an instrument for measuring angles. Contact goniometers have two metal rules pivoted at the center of a graduated semicircle. The device is positioned perpendicular to the edge between two crystal faces, and the rules are brought into contact with the faces to measure the angle between them. Reflecting goniometers are precise instruments used to measure angles on small crystals with smooth faces.
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What are some different types of goniometers and how are they used in science or medicine?
A goniometer is an instrument for measuring angles. Types of goniometers include contact, reflecting, two-circle, and three-circle.
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Contact goniometers are used for approximate measurement of large crystals. They consist of two metal rules pivoted at the center of a graduated semicircle.
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Reflecting goniometers are used for accurate measurement of angles on small crystals with smooth faces. The crystal is turned, and the angle is determined by a graduated circle.
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Two- and three-circle goniometers allow for measuring angles between zones of crystal faces without readjustment.
In mineralogy and geology, reflecting goniometers measure angles between crystal faces to identify a mineral's crystal system. An ordinary microscope fitted with cross wires and a rotating graduated stage serves the purpose of a goniometer for measuring the plane angles of a crystal face or section.
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goniometer, instrument for measuring angles, particularly used in the study of crystals. Nicolaus Steno in 1669 determined the interfacial angles of quartz crystals by cutting sections perpendicular to the edges, the plane angles of the sections being the angles between the faces which were perpendicular to the sections. The earliest instrument used to measure these angles was the contact goniometer devised by Arnould Carangeot in 1783.
Contact goniometers
A contact goniometer consists of two metal rules pivoted together at the centre of a graduated semicircle. The instrument is placed with its plane perpendicular to an edge between two faces of the crystal to be measured, and the rules are brought into contact with the faces. The angle between the rules, as read on the graduated semicircle, then gives the angle between the two faces. The rules are slotted, so that they may be shortened and their tips applied to a crystal partly embedded in its matrix. The instrument illustrated is employed for the approximate measurement of large crystals.
Reflecting goniometers
The reflecting goniometer is an instrument of far greater precision and is used for the accurate measurement of the angles when small crystals with smooth faces are available. Such faces reflect sharply defined images of a bright object. By turning the crystal about an axis parallel to the edge between two faces, the image reflected from a second face may be brought into the same position as that formerly occupied by the image reflected from the first face. The angle through which the crystal has been rotated, as determined by a graduated circle to which the crystal is fixed, is the angle between the normals to the two faces.
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Several forms of instruments depending on this principle have been devised. The earliest type consisted of a vertical graduated circle reading degrees and minutes, which turned about a horizontal axis. A great improvement was effected by placing the graduated circle in a horizontal position. Many forms of the horizontal-circle goniometer have been constructed: they are used on telescopes and collimators, and in construction they are essentially the same as a spectrometer, with the addition of arrangements for adjusting and centring the crystal on a stage on the horizontal circle. Light from any convenient source is passed through the slit of the collimator and the image reflected from the crystal face is viewed in the telescope. The crystal holder can be adjusted to bring the image exactly on the cross wires of the telescope. The circle can then be rotated until the image from a second crystal face is brought on the cross wires of the telescope. The angle through which it has been turned is the angle between the two face normals.
However, with a horizontal-circle goniometer, it is necessary to mount and readjust the crystal for the measurement of each zone of faces (i.e., each set of faces intersecting in parallel edges). Further, in certain cases, it is not possible to measure the angles between zones. These difficulties have been overcome by the use of a two-circle goniometer. The crystal is set up and adjusted with the axis of a prominent zone parallel to the axis of either the horizontal or the vertical circle. The positions of the faces are fixed by the simultaneous readings of the two circles. Some disadvantages are overcome by adding still another graduated circle to the instrument, with its axis perpendicular to the axis of the vertical circle, thus forming a three-circle goniometer. With such an instrument measurements may be made in any zone or between any two faces without readjusting the crystal. Goniometers have been devised for measuring crystals during their growth in the mother liquor and for cutting section plates and prisms from crystals (precious stones) accurately in any desired direction. An ordinary microscope fitted with cross wires and a rotating graduated stage serves the purpose of a goniometer for measuring the plane angles of a crystal face or section.
Weissenberg X-ray goniometers
The Weissenberg X-ray goniometer is used in recording X-ray reflections from crystals. The crystal oscillates through about 200° around an edge, as a cylindrical camera is translated back and forth parallel to the crystal rotation axis. In Martin Julian Buerger’s design the angle which the rotation axis makes with the X-ray beam is variable.