This instrument is catalogued as a telescope, but in reality it is a transit circle.
Still in use for the determination of equatorial coordinates (right ascension and declination) of celestial bodies, the transit circle is one of the fundamental instruments in the compilation of star catalogues.
A transit circle is essentially composed of a telescope that can rotate around a horizontal axis perpendicular to its own optical axis and a graduated circle, orthogonally attached to the rotation axis, which is oriented in the east-west direction. There is a reticle on the focal plane of the objective; it is composed of an odd number of vertical hairs and one or more horizontal hairs and can be shifted or rotated slightly to place the central vertical hair on the meridian.
The equatorial coordinates of a star on the celestial sphere, which are determined with the transit circle, are the analogues of the geographical coordinates of a place on the earth's surface. ...continues