A brass quadrant, nocturnal, and Regiment of the Pole Star, probably English, late 16th-Century.

Details

A brass quadrant, nocturnal, and Regiment of the Pole Star, probably English, late 16th-Century.
The quadrant
One side is marked with a small shadow square and below this an horological quadrant. Both are used with a pair of pin-hole sights; the hole for the plumb-line is at the apex, but there is no line present. The shadow square is divided along each edge in units to 6 at the 45 position. The arc of the quadrant is divided in single degrees which are labelled in tens to 90. Immediately above the degree scale is the solar altitude scale divided into five-day intervals from 10 December to 10 June, hat is from the Winter Solstice to the Summer Solstice. These dates mean that the Julian, or Old Style, calendar was being used. The placing of this altitude scale lies between 14 and 61, which means the quadrant is for use at the latitude 52.
The hour lines have become faint through polishing, done most likely during the past century. The lines give the equal hours from 4 to 12 noon, and then to 8 in the evening; their form is that of Stffler (1561). Just visible is the wide curve of the ecliptic line that is marked at either end and in two places along its length with the symbols of the Zodiac.

The nocturnal and Regiment of the Pole Star
The outer edge is divided into the twelve signs of the Zodiac, each with 30 numbered in tens, labelled with the names and the symbols. There follows the calendar, in units of one day numbered in tens (or to 28 and 31), with names in English. The third band provides the age of the Moon, 0-29 days beginning and ending at the handle. This position is also marked in 12s, meaning the Moon is due south at 12 o'clock. At each following day there is an increment of 48 minutes in the time the Moon is south. The phase of the Moon is simulated by the aperture in the volvelle that rotates about the centre of the disc.
The volvelle has two indexes, the longer is engraved with a hand, and points to the position of the Sun in the Zodiac. On the opposite side an index points to the age of the Moon. The edge of the volvelle is marked out in twice twelve hours.
The central part is engraved with eight points of the compass and a band of degrees in four sequences from 0 to 4 9'. Across the band is a set of parallel lines connecting like numbers. It is this part that gives the measure of difference between the altitude of the true North Pole from the altitude, as measured, of Polaris (UMi). An adjustment is necessary because Polaris appears to rotate about the true Pole, so when it is North or South of the Pole, about 4 has to be subtracted or added to the altitude as measured by a quadrant, and when East or West no correction need be made to the value obtained for the altitude. Originally a curved arm would have been attached to a boss at the centre. This arm, known as 'the Horn', represented the constellation of Ursa Minor, with Polaris at one end and the 'guard' Kochab (UMi) at the other. It is possible to see where this curved arm was originally attached.
The star Kochab also serves as an indicator when the instrument is used as a nocturnal. When the handle is held vertically, the meridian line passes through 9 Scorpio (22 October), which is correct for the period -- 56in. (13.2cm.) diameter

See Colour Illustration and Details

Literature

STFFLER, Johannes, Elvcidatio fabricae vsvqve astrolabii (Oppenheim, 1524)
WATERS, D.W., The Art of Navigation in England in Elizabethan and Early Stuart Times (London, 1958) pp.45-6

Lot Essay

The maker of this instrument is unknown. The letters and numerals, for example the shape of 1 and 8, with a reversed S for South on the volvelle, do not match any known craftsman. The mathematical lines are scratched rather than engraved in the normal manner. Nevertheless, this is an item of considerable interest. Not only is the Regiment of the North Star provided, but it has an early, and erroneous, Polar Distance of 4 9'. The customary value became 3. It is worth giving Cdr Water's explanation, which makes the position clear:

..the earliest detailed description of [an instrument] in print appears to be contained in Martin Cortes's Arte de Navegar, written in 1545, published in 1551. This consisted of a disc or volvelle marked with the four cardnal points termed also 'The Head', 'The Foot', 'The Right Arm' and 'The Left Arm', with an inner circle drawn on it marked with the degrees of correction to be applied to the Pole Star to find the true Pole. The navigator rotated a pointer in the form of a trumpet, marked with the seven stars in the constellation of Ursa Minor, until it coincided with the position of Ursa Minor, holding the instrument up meanwhile and sighting the Pole Star through a hole in the centre. ... Unfortunately he used the astronomer Werner's erroneous (1541) Polar Distance of 4 9' instead of the seamen's more accurate 3 30' of that time.

The first English edition of the book by Cortes was published at London in 1561.

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