Bright and conspicuous stars[230] which are _not far distant from the equator which it will be useful to observe at their rising and setting: the amplitude at the Horizon on rising being known from the altitude of the pole and from the declination of the stars, by means of a globe, or tables, or an instrument whence the variation is perceived by technical calculation._ {175} _Right Ascension_ _Declination_ |Oculus Tauri | 62° 55' | 15° 53' N | |Sinister humerus Orionis | 72° 24' | 4° 5' N | |Dexter humerus Orionis | 83° 30' | 6° 19' N | |Præcedens in cingulo Orionis | 77° 46' | 1° 16' S | |Canis major | 97° 10' | 15° 55' S | |Canis minor | 109° 41' | 5° 55' N | |Lucida Hydræ | 137° 10' | 5° 3' S | |Caput Geminorum australe | 110° 21' | 28° 30' N | |Caput boreale | 107° 4' | 32° 10' N | |Cor Leonis | 146° 8' | 13° 47' N | |Cauda Leonis | 171° 38' | 16° 30' N | |Spica Virginis | 195° 44' | 8° 34' S | |Arcturus | 29° 13' | 21° 54' N | |Cor Aquilæ | 291° 56' | 7° 35' N | _An instrument for finding the amplitude at rising on the horizon._ Describe the circumference of a circle and let it be divided into quadrants by two diameters intersecting each other at right angles at its centre. One of these will represent the æquinoctial circle, the other the axis of the world. Let each of these quadrants be divided (in the accustomed way) into 90 degrees; on every fifth or tenth of which at each end of each diameter and on each side let marks (showing the numbers) be inscribed on the two limbs or margins made for that purpose outside the circumference. Then from each degree straight lines are drawn parallel to the æquator. You will then prepare a rule or alhidade equal to the diameter of that circle and divided throughout into the same parts into which the diameter of the circle representing the axis of the world is divided. Let there be left a small appendage attached to the middle of the rule, by which the middle of the fiducial line itself of the rule may be connected with the centre of the circle: but to every fifth or tenth part of that rule let numbers be attached proceeding from the centre toward each side. This circle represents the plane of the meridian; its centre the actual point of east or west, _i.e._, the common intersection of the horizon and æquator; all those lines æquidistant from the æquator denote the parallels of the sun and stars; the fiducial line of the rule or alhidade represents the horizon; and its parts signify the degrees of the horizon, beginning from the point of setting or of rising. {176} [Illustration]