Sutton’s or Collins’s quadrant is a stereographic projection of the quarter of the sphere between the tropics of the plane of the ecliptic the eye being in its north pole. It is fitted to the latitude of London. The lines running from the right hand to the left are parallels of altitude & those crossing them are azimuths. The smaller of the two circles bounding the projection is one fourth of the tropic of Capricorn the greater one fourth of that of Cancer. The two ecliptics are drawn from a point in the left edge of the quadrant with the characters of the signs upon them & the two horizons are drawn from the same points. The limb is divided both into degrees and time by having the sun's altitude the hour of the day may be found here to a minute. The quadrantal arches next the centre contain a calendar of months & under them in another arch is the sun’s declination. On the projection are placed several of the most fixed stars between the tropics.
For the manner of using the quadrant turn over
[To] find the time of the sun’s rising or setting, his amplitude, azimuth, hour of the day &c by this quadrant: lay the thread over the day and the month, and bring the bead to the proper ecliptic, either of summer or winter; then moving the thread then moving the thread, bring the bead to the horizon, in which case the thread will cut the limb in the time of the sun’s rising, or setting, before or after 6, and, at the same time, the bead will cut the horizon in the degrees of the Sun’s amplitude.
Observing the Sun’s altitude with the quadrant and supposing its found 45° on the 5th pf May; lay the thread over the 5th of May, bring the bead to the Summer ecliptic, & carry it to the parallel of altitude 45° in which case the thread will cut the limb at the 55° 15’, & the hour will be seen among the hour lines to be either 41’ past 9 in the morning or 19’ past 2 in the afternoon; lastly the bead among the azimuths shows the sun’s distance from the south 50° 41’.
If the Sun’s altitude be less than it is at 6 o’clock the operation must be performed over the upper horizon i.e. among those parallels above the upper horizon.