The declination is the angular distance of a star from the celestial equator in the direction of the poles and it is immediately seen that it is the analogue of the latitude. With the aid of the micrometers placed on the columns holding the instrument, the zenith distance is measured on the graduated circle and from this, knowing the latitude of the place of observation, the declination can be calculated.
The right ascension is the analogue of the longitude, but it is measured in hours, minutes and seconds; it is determined by finding the instant at which the passage of the star at the meridian takes place. This is performed by using, together with the transit circle, a clock set by sidereal time.
The following are missing in the exemplar presented: the lateral graduated circle, the micrometers, the reticle and the semi-transparent mirror for illuminating it, which was at the centre of the eyepiece tube between the two lateral arms.
It lies on a heavy cast iron stand composed of two vertical buttresses (height 50.5 cm) on a rectangular base (58 x 18.5 cm).
The telescope tube is cylindrcal (length 80.4 cm; diameter 58.5 mm) and the two side arms are hollow and in the form of a truncated cone (overall length 47 cm, diameter of each 9.5 cm and 3 cm; the tube and the two arms are connected to each other and communicate at the centre. ...continues