This device is not otherwise mentioned in the literature, and its originality is doubtful, since as early as 1810 Malus constructed a horizontal circle goniometer with observation telescopes.
No goniometer with a horizontal circle and mirror is known to the author, but Mallard illustrated one in 1879, and professor William Hallowes Miller (1801-1880) of Cambridge, for whom the currently used crystal indices ("Miller indices") are named, published a description of such a goniometer, manufactured by Troughton & Simms, in 1876.
All of these disadvantages can be avoided by the use of a horizontal circle.
Strictly for historical reasons, the introduction of observation telescopes in vertical and horizontal circle goniometers will be described separately: Malus's goniometer first and Mitscherlich's second.
The Malus goniometer has a horizontal circle, and a straightedge, rotatable about the circle axis, on which the crystal is actually mounted.
The horizontal circle H is divided into single degrees, and may be read to half a degree with the aid of an indicator a.
The horizontal circle H corresponds to the equator on a globe, the vertical circle a meridian and its 0 point the north pole.
The horizontal circle readings are recorded at the point at which the gyro mark reverses direction.
The observer then enters four horizontal circle readings, two on face II and two on face I, taken to the Reference Object (RO).
Repairing & Servicing of Autolevels (Temporary adjustment (Level screw, tribach plate & trivet plate), Permanent adjustment, Line of collimation, Line of sight, Visibility of cross hair on reticule, Focusing of eyepiece and objective lenses, Removal of parallax, Bubble in spirit level, Horizontal tangent screw, Focusing knob, Removal of zero error in horizontal circle
gradation, Compensator mechanism (pendulum prism) etc)