Probably North Italian, first half of the 14th century

The Property of a Distinguished English Family

Probably North Italian, first half of the 14th century

Astrolabe

with an added English plate for London and Lincoln

copper alloy

including shackle: 29cm., 11⅜in.

diameter: 22cm., 8⅝in.

Rete

The elegantly restrained strapwork consists of a quatrefoil within the upper centre of the ecliptic circle with a demi-quatrefoil, also centrally placed, beneath the arc of the equator. The positions of 42 stars are marked by lightly curved pointers. These are (in the listing by order of increasing mediation given in Davis et al):

Mirac  / β Andromeda / Pantak / ζ Cetus / Enif / α Aries

Finis fluxus / η Eridanus / Menkar Cetus / Algenib / α Perseus

Augetenar / γ Eridanus / Aldebaran / α Taurus / Alhay / α Aurigae

Rigil / β Orionis / α Algevze / Orionis / not named

Alhabor / α Canis Ma / Algomeyza / α Canis mi / Markeb / ρ Pup

Egreges / μ Ursa ma /  Aldiran / Leo / Alfart / α Hya

Cor Leo / α Leo / Alrucaba / ν Ursa Ma / Corvus / ghost

Dvbhe / α Ursa Ma / Cauda Leo / β Leo / Alchimec / α Virgo

Benenas / η Uma / Alramec / α Boötes / Alfeca / α CrB

Yed / δ Ophiucus / Cor scor / α Scorpio / Alhave / α Ophiucus

Razta / γ Draconis / Vega / α Lyra / Altayr / α Aquilonis

Delfi / ε Delphinus / Adige / α Cygnus / Libe / δ Capricornus

Aldiran / α Cepheus / Denebal / δ Capricornus Crvs / δ Aquarius

Alfer / β Pegasus / Denbk’ / ι Cetus / Sceder / α Cassiopeia

The ecliptic ring carries the names for the signs (some abbreviated), each divided by numbered groups of ten degrees and with division lines carried over onto the edge. There is a neatly chamfered, lobed but almost triangular Capricorn pointer, and the ends of the Capricorn ring are worked with a stylised dragon head and tail. The vertical bar that runs from the ecliptic ring to the lower equatorial arc has snapped, at the point where it meets the ecliptic circle. It is however still in position 

Mater

This is composed of three circular layers with an extension forming the throne, these are the backplate itself and two rings. The upper of these is engraved with the scales described below. The plate itself is blank.

Limb

This carries a full 360° scale divided to 1° by numbered groups of ten. The zero position beneath the throne is marked by a small dot indentation, and this is repeated every 15°, thus marking the hours in an economical, but very unusual way.

Throne

This is of a double lobe form with shoulders. On the face an engraved arc carries the circle of the lower lobe to beneath the shackle. This latter is of ‘U’ form and two suspension rings are attached to it.

Back

Reading inwards from the circumference, the back is engraved with a degree scale in four quadrants 90-0-90-0-90 reading to one degree by numbered groups of 10. Within this is a zodiacal calendar (0° Aries = almost 12 March) with the month ring placed eccentrically. Within this in the upper half is an unequal hour diagram, and in the lower half, a shadow square of twelve, numbered by groups of four. Inside the shadow square, a later hand has added, rather crudely, the inscription in (partly) hollow capitals, ‘I LOND’ using a reversed ‘N’.

Plates

There are four plates for latitudes

37° Carthage and 38° Tunis

41° Armenia and 42° Rome

45° Cremona and Paris 49°

52° London and Lincoln 53°

Each is engraved with circles for the tropic of Cancer and the Equator; with almucantars drawn at 2° intervals numbered every 6°; with azimuths drawn at 10° intervals; and with arcs for the unequal hours beneath the horizon.

Given that the metal analysis, the thickness, and the script of the London/Lincoln plate are significantly different from that of the other three, it is clear that this plate was produced in a different workshop. This, given that the cities for which it is drawn and that the metal profile is similar to that of attested English instruments from the same period, was probably in England, at a date only slightly later than that of the rest of the instrument.

Components

While the alidade and shackle conform in metal analysis with the rest of the instrument, the rule and the pin have a different chemical profile and are later replacements.