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Instrument type

Signed by Regnerus Arsenius
Dated 1565; Louvain
Gilt brass; 297 mm in diameter

The astrolabe is finished in gilt and finely engraved throughout, on the front with a common stereographic projection, on the back with a universal projection of the Gemma Frisius type, and on the inside of the mater with a quadratum nauticum.

The rete is strapwork and incorporates the tulip motif typical of Flemish astrolabes of the period. The stars are named with their planetary temperaments and magnitudes and are, with a few exceptions, numbered on the back of the rete, where extensive constructions marks, in the form of graduated and ungraduated arcs, are also visible.

Only a single plate is present, for the latitudes 45 and 51? north. The regula, cursor and brachiolus required for use with the universal projection on the back are absent, an alidade alone being provided, for use on the front. Whether the astrolabe was ever provided with a regular, cursor and brachiolus remains, as will be discussed subsequently, a matter of doubt, as the back of the instrument is significantly concave towards the centre: a characteristic that would make the satisfactory use of any form of flat rule on the back extremely difficult.

A further peculiarity of the astrolabe is the throne: as is typical in Arsenius astrolabes post-1558 this is cast in the form of two satyrs, male and female; unusually however, a heraldic centrepiece is placed between the satyrs, replacing the compass otherwise typical of almost all other instruments by Arsenius from the period.

The details of the scales engraved on the astrolabe are as follows. The face of the limb is engraved with the cardinal points, and three circular scales. The four cardinal points are named, clockwise from below the throne: 'MERIDIES', 'OCCIDENS', 'SEPTENTRIO' and 'ORIENS', the latter three being oriented with their baseline towards that outside of the of the astrolabe, 'MERIDIES' with its baseline towards the inside, thus right-reading as one would naturally hold the instrument. Lines marking the cardinal directions, extending from those on the latitude plate, divide the limb into four quadrants and bisect the names of the cardinal directions, albeit somewhat asymmetrically, especially in the case of 'ORIENS', which is split 'ORIE' and 'NS'.

The three circular scales on the face of the limb are, from the outside in: a scale of equal hours, a scale of degrees, and a circular shadow scale.

The scale of hours is numbered I to XII twice, once every each 180?, clockwise, beginning directly below and opposite the throne. The fourth hours are here given in the additive form 'IIII', as they are throughout the instrument. The numbers for the hours are oriented with their baseline towards the centre of the instrument and are right-justified against the principal hourly divisions of the scale, which is further divided every four minutes.

The scale of degrees begins 90? clockwise of the throne, increases anticlockwise, is divided by 10, subdivided every 5? and 1?, and is numbered by 10 with the numbers oriented with their baseline towards the centre of the instrument and left-justified against the principal divisions.

The circular shadow scale (a non-linear scale of tangents) is divided and numbered 1 to 12 to 1 fours times (once in each quadrant), is subdivided to 1/5s, and is named in every quadrant 'VMBRA RECTA', 'VMBRA VERSA'. The numbers and labels are oriented with their baseline towards the outside of the instrument and are right-justified against the principal division in one half of each quadrant, left-justified in the other half, with the figure '12' spanning the division that it marks in each case, a division that is also marked with what is presumably meant to be a sun symbol: [Sun].

The inside rim of the limb sports a rectangular notch for the tab of the latitude plate immediately below the throne but is otherwise unengraved, as is the outside rim of the limb, except for a hairline-weight construction mark in the form of the symbol [Aries] just visible positioned adjacent to the first point of Aries in the zodiacal-calendar scale on the back of the instrument.

The inside of the mater is engraved with a north-south line, east-west line, and a quadratum nauticum. The Quadratum Nauticum', thus labelled, is placed inside a ring that is engraved as a double (circular) line and inset from the inside rim of the limb by a distance equal to the width of the limb. Surrounding the main body of the quadratum nauticum are engraved the names of the cardinal directions 'MERIDIES', 'OCCIDENS', 'SEPTENTRIO' and 'ORIENS', each with their baselines in the same orientation, towards the bottom of the instrument. The outside border of the quadratum nauticum is made-up of four scales, 90 to 10 and 10 to 90 along each side, divided by 10, subdivided by 5 and numbered by 10. The numbers on the top and bottom sides read right when the astrolabe held normally; those on the left and right sides are oriented with their baselines towards the outside of the instrument. The numbers are justified on the inside of the principal divisions from the point of view of the mid-point of each side of the square. They are labelled: 'Longitdo vel maior Orientalior', 'Latitudo minor siue Australior', 'Longitudo minor aut Occidentalior', and 'Latitudo maior aut Borealior', these labels being placed on the horizontal side of the north-west quadrant of the quadratum nauticum, on the vertical side of the north-east quadrant, on the horizontal side of the south-east quadrant, and on the vertical side of the south-west quadrant, with their baselines in the same orientation as those of the numbers on the scales.

The four corners of the quadratum nauticum touch the inside of the circular bounding ring. Lines marking the 90 division at the end of each scale extend to the outside circumference of this ring. The central square of the quadratum nauticum, within the scales forming its four side, is divided into 36 smaller squares, 6 ? 6, and by 32 radial directions, each of which is named in Latin with its corresponding wind. The names of the winds are arranged in three groups relative to a circular band, the outer circumference of which touches the inside of the four scales at a tangent, and the width of which is the same as 10 divisions of the square outer scales. Within the circular band itself are named the following winds, clockwise from below the throne: 'Auster','Libonotus', 'Africus', 'Zephirus', 'Corus', 'Circius', 'Aparctias', 'Aquilo', 'Cecias', 'Subsolanus', 'Vulturnus' and 'Euroauster'. Each is oriented with its baseline towards the centre of the instrument. In the four spandrel spaces formed by the circular band are the winds 'Lebeccio', 'Magistralis', 'Greco' and 'Syrocho', in the north-east, south-east, south-west, and north-west squares of the quadratum nauticum respectively. Again, each is oriented with its baseline towards the centre of the instrument. The remaining winds are given in the space inside the circular band. They are, clockwise from below the throne: 'Mediojorno', 'Lebeche mediojorno', 'Lebeche', 'Poniente lebeche', 'Poniente', 'Poniente maestre', 'Maestral', 'maestre tramontana', 'Tramontana', 'Grego tramontana', 'Grego', 'Grego leuante', 'Leuante', 'Xaloque leuante', 'Xaloque', and 'Xalogue [sic] mediojorno'. Each label is oriented with its baseline anticlockwise of the label itself. Small arrows pointing towards the centre of the astrolabe, and touching the outer circumference of the circular band with the points of their arrowheads, are placed at the 30? and 60? points of each quadrant of the circular band, thus dividing it into equal sectors of 30?.

The throne, as has previously been mentioned, consists of two satyrs of youthful complexion and a heraldic centrepiece. The satyrs are cast in one piece with the curved bar, slightly trapezoid in section, that forms the base of the throne. This is attached to the mater of the astrolabe by three screws: two separate screws with octagonal heads at the ends of the base, and one screw integral with the throne itself exactly at the centre of the base. (In order to separate the throne from the mater, not only must the octagonal-headed screws be removed but the whole of the throne itself rotated to detach it from the mater.) The holes for all three screws, which are conical, pierce the inside rim of the limb.

The heraldic centrepiece is a separate casting from the rest of the throne and is attached to the base by two small steel lugs with Whitworth metric threads. On both sides it bears, according to Gunther, 'a coat-of-arms azure, two bars gules, between stars 3, 2, and 1, which corresponds closely with the coat borne by the Frisian family of Schenckels'. Above the coat of arms is a circular hub, decorated with eight small rivet heads, connecting to a further throne-piece which supports a swivel pin and a large suspension ring.

The rete of the astrolabe is formed in strapwork and contains the tulip motif typical of Arsenius and the Flemish workshops. It bears 55 flame-shaped star-pointers, numbered on the back of the rete. Engraved at the base of each star-pointer is the name of the star, the star's planetary temperaments, and its magnitude, as follows: 1. 'Cauda [Capricorn] [Saturn] [Jupiter] [Mercury] 3'; 2. 'Crus [Aquarius] [Mercury] [Saturn] 3'; 3. 'Cauda ceti [Saturn] 3'; 4. 'Venter ceti [Saturn] 3'; 5. 'Nares ceti [Saturn] 3'; 6. 'Oculus [Taurus] [Mars] 1'; 7. 'Orionis sinister humer[9] [Mars] [Mercury] 2'; 8. 'Orio: sinis: pes [Jupiter] [Saturn] 1'; 9. 'Orio: dex: hume: [Mars] 1'; 10. 'Canis maior [Jupiter] [Mars] 1'; 11. 'Canicula [Mercury] [Mars] 1'; 12. Cor [Leo] [Jupiter] [Mars] 1'; 13. 'Hydre clara [Saturn] [Venus] 2'; 14. 'Crateris fundus [Venus] [Saturn] 4'; 15. 'Spica virginis [Venus] [Mercury] [Jupiter] 1'; 16. 'Cor [Scorpio] [Mars] [Jupiter] 2'; 17. 'Ophiuchi ma: dex: 4'; 18. 'Ophiuchi caput [Saturn] [Venus] 2'; 19. 'Caput herculis [Mars] [Mercury] 3'; 20. 'Caput draconis [Saturn] [Mars] 3'; 21. 'Ophiuc: sinis: manis 3'; 22. 'Corona septentri: [Venus] [Mercury] 2'; 23. 'Lanx boree clarior [Jupiter] [Mercury] 2'; 24. 'Bootis sinister humerus [Jupiter] [Saturn] 3'; 25. 'Arcturus [Jupiter] [Mars] 1'; [26 to 32 (unnumbered)]. 'Ursa ma -ior [Mars] 2'; 33. 'Cauda leonis [Mars] 2'; 34. 'Hircus [Mars] [Mercury] [Jupiter] 1'; 35. 'Meduse caput [Saturn] [Jupiter] 2'; 36. 'Cassio: pec'; 37. 'Pegasi vmbili:'; 38. 'Crus pegasi [Mars] [Jupiter] 2'; [3]9. 'Pegasi humerus [Jupiter] [Mercury] 2'; 40. 'Cauda cygni'; 41. 'Aquila [Mars] [Jupiter] 2'; 44. 'Cephei dex hume:'; 45. 'Andro: [obar]bili: [Venus] 3'; 46. 'Persei lat' dex: [Jupiter] [Venus] 2'; 50 or 58. 'Ophiuc: genu sinis:'; 51. 'Caput [Gemini] antecedentis [Jupiter] [Saturn] 2'; 53. 'Corui ala dextra [Saturn] [Mars] 3'; 57. 'Ophiuchi genu dex: [Saturn] 3'; 60. 'Cinguli orio: media 2'; 63. 'Dexter hume: [Aquarius] [Mercury] [Saturn] 3'; 64. 'Sinister hume [Aquarius] [Mercury] 3'; 68[?]. 'Pegasi rictus [Mars] [Mercury] 2'; [not numbered]. 'Dorsum leonis [Saturn] 2'; [not numbered]. 'Lyra [Venus] Mercury 1'; and [obscured by plug]. 'Ala Pegasi [Mars] [Jupiter] 2'.

The ecliptic circle is marked with a non-linear scale of degrees divided, as is customary, into the twelve signs of the zodiac, each of which is subdivided by 10, by 5, and by 1, and numbered by 10 from 10 to 30. The division by single degrees extends onto the fiducial edge of the ecliptic circle. The signs are marked with their usual names, in an uppercase semi-italic, and with their symbols. The second 'T' in 'SAGITTARIVS' is somewhat smaller than the first - a feature common to other Arsenius astrolabes.

The back of the rete is, as previously mentioned, engraved with the numbers of the star pointers and with circular arcs, both graduated and ungraduated. The scheme of the numbering begins by following an anticlockwise pattern outside the ecliptic circle before become more irregular. The circular arcs not only mark the position of the ecliptic and its division, but also the key characteristics of the shape of strapwork, so betraying its regular underlying geometrical basis.

The single plate now with the astrolabe is laid out on one side for a latitude of 45? north, labelled 'Pro eleua: poli 45', and on the other side for a latitude of 51? north, labelled 'Pro eleua: poli 51'. Both sides of the plate are marked with (celestial) north-south and east-west lines and with circles for the equator: '? quinoctialis' and '? quinoctia:' respectively; the tropic of cancer: 'Tropicus cancri' and 'Tropi: cancri' respectively; and the tropic of capricorn: 'Tropicus capricorni' and 'Tropic: capricorni' respectively. On both sides the east, west and north directions are marked: 'Ories', 'Occides' and 'Septentrio', and 'Oriens', 'Occides' and 'Septentrio' respectively, as are the two horizons: 'Horizon rect:' and 'Horizon obliguus', and 'Horizon rectus' and 'Horiz[obar] obliguus [sic]' respectively.

Both sides of the plate are marked with the astrological houses according to the manner of Regiomontaus, numbered 1 to 12 anticlockwise from the horizon rectus with the baselines of the numbers oriented towards the outside of the plate, and with lines for unequal hours, numbered I to XII clockwise from the horizon obliquus with the baselines of the numbers oriented towards the centre of the plate. The lines marking the houses, as well as the north-south and east-west lines, on both sides of the plate, extend beyond the tropic of capricorn to edge of the plate, the hours lines only to the tropic. The plate has a rectangular tab at its south point.

On both sides of the plate azimuths are provided every 5 degrees to 80? of declination, every 10 degrees to 85?, and every 30 degrees from 85? to the pole. Almucantars are provided every degree. The azimuths are numbered by 10 from 10 to 90 to 10 along the horizon, and by 10 from 10 to 90 to 10 in an arc following the 22? almucantar. The numbers on the horizon are placed with their baselines towards the horizon, those following the 22? almucantar with their baselines towards the pole. The division lines that they mark bisect the numbers. The almucantars are numbered in three arcs: by 10 from 80 to 20 along an arc from the pole southwards along the meridian; by 10 from 80 to 10 along an arc from the pole to the east point on the horizon; and by 10 from 80 to 10 along an arc from the pole to the west point of the horizon. The numbers in the first arc are placed west of the of the meridian with their baseline away from it, those in the remaining two arcs below the arcs with their baselines away from the arcs.

The grid formed by the almucantars and azimuths is punctuated by punch marks every 10 degrees of right ascension between 10 and 80 degrees declination, in the form of short straight bars running in the direction of the almucantars which are themselves composed of two tiny isosceles triangles with their apexes touching. The unequal hours are punctuated with similar punches, running in the direction of the hour lines. Both plates are also marked with a series of dots (every degree) running southwards along the meridian from the 80? almucantar to a point equal to the latitude for which the particular side of the plate is drawn, i.e. to 45? on one side, 51? on the other.

The back of the astrolabe is engraved with a universal projection of the Gemma Frisius type, contained within a zodiacal-calendar scale.

The zodiacal-calendar is orientated with the baseline of all labels and numbers towards the outside of the instrument. The calendar scale is outermost and is divided into the 12 months, subdivided every 10 days, 5 days and every day. The 10th day, 20th day and last day of every month are numbered, with the numbers right-justified against the division, that is, against the start of the day. The months are numbered I to XII beginning with January and are named in Latin thus: 'IANVARIVS', 'FEBRVARIVS', 'MARTIVS', 'APRILIS', 'MAIVS', 'IVNIVS', 'IVLIVS', 'AVGVSTVS', 'SEPTEMBER', 'OCTOBER', 'NOVEMBER', 'DECEMBER'. The year is 3641/4 days long and the 11th March corresponds to the Vernal equinox and first point of Aries.

The zodiac scale is divided every 30? into the 12 signs of the zodiac, subdivided by 10, by 5 and by 1. Each sign is numbered by 10 from 10 to 30, with the numbers right-justified against the principal divisions. The signs are numbered 1 to 12 beginning with Aries, are marked with their symbols and are named conventionally, thus: 'Aries', Taurus', 'Gemini', 'Cancer', 'Leo', 'Virgo', 'Libra', 'Scorpius', 'Sagittarius', 'Capricornus', 'Aquarius', 'Pisces'.

The universal grid itself has the customary pattern of lines of right ascension and declination expected of a projection of the Gemma Frisius type. Lines of right ascension are engraved every degree as far as the declinations 70? north and 70? south. From there they continue every two degrees as far as 80? north and south, from there, with the exception of those 10? east and west of the meridian, every five degrees to 85? north and south, and from there every 10? to the poles. There is some minor variation of this pattern, as some of the lines of right ascension appear to extend slightly beyond others, on a fairly arbitrary basis depending on the engraved clarity of the particular line. This pattern of lines as they end towards the poles is one of the characteristics that lends the projection, and thus the astrolabe, much of its elegance.

In addition to these regular gridlines, the tropics are marked, as are the polar circles. Only the lines of declination are numbered: every 10? from 10 to 90 four times anticlockwise beginning below the throne. The numbers are right-justified against the divisions marking every 10th degree, which themselves extend beyond the main body of the grid to the inner circumference of the zodiacal scale. The grid is punctuated every 10 degrees on the intersection of every 10th degree line of declination and right ascension with punched chevrons, and every 10 degrees offset by 5 degrees by half chevrons below 70? north and south. Between these punches are arrowheads pointing north. Between 80 and 90? south on the meridian oblique strokes are engraved running in the direction north-west to south-east. There is also a small circular punch mark at 19 ? north by 15 ? west and a smaller one still at 10 ? north 5 ? west. Dotted lines which peter-out gradually extend from both poles towards the circumference of the astrolabe along the meridian line where it passes through the zodiacal-calendar.

The following stars are marked (by the symbol g) and named on the universal projection: seven stars of 'Vrsa maior', 'Lyra', 'Cauda cigni', 'Hircus', 'Aquila', 'Arcturus', 'Spica [Virgo]', 'Cor [Leo]', 'Oculus [Taurus]', 'Canicula', 'Orio: dex: hume', 'Cauda [Scorpio]', 'Postre: aque fuse', 'Canis maior', 'Eridani extrema', and 'Canopus'. All are oriented with their baseline towards the bottom of the astrolabe. The ecliptic line is divided every 30? into the signs of the zodiac with 'T' shaped dividing lines (in the manner of error bars in a bar graph) with each sign further divided into three with two half-sized 'T' lines at the 10 and 20? points. The ecliptic line is further subdivided by 5 and finally by 1, this time with the usual straight divisions. Each sign is numbered by 10 from 10 to 30, with the numbers right-aligned against the appropriate divisions. Each sign is marked only by the symbol of the corresponding sign of the zodiac, centre-justified in the first 10? of the sign and oriented with their baseline towards the central line of the ecliptic.

The tropics are marked with hours, 1 to 12. Those on the tropic of cancer appear the right way up as the astrolabe is held normally; those on the tropic of capricorn upside down. There is no division of the tropics beyond that provided by the grid of the universal projection.

The alidade of the astrolabe is counter-changed. It is engraved on one arm with a scale of Italian hours and a scale of Babylonian hours, on the other with scales of declination north and declination south. The scale for declination north is marked 'Declinatio Septentrionalis' and is a non-linear scale from 10 to 70, beginning a third the way along the arm from the tip and increasing to the centre, divided by 10 and subdivided by 5 on the fiducial edge, numbered by 10 with the numbers right-justified against the principal divisions and their baseline towards centre-line of the arm. The scale for declination south is marked 'Declina: Meridionalis' and is a non-linear scale from 10 and 20 towards the tip of the alidade, divided by 10 and subdivided by 5 on the fiducial edge, numbered by 10 with the numbers right-justified against the principal divisions and their baseline towards the edge of the arm. On the other arm, the scale of Italian hours is marked 'Hor? [Sun] ortus' and increases linearly from 1 to 10 towards the centre of the alidade starting from a point a third the way along the alidade from the tip. It is divided by 1, subdivided by 1/2 on the fiducial edge, and numbered by 1 with the numbers right-justified against the principal divisions and their baseline oriented towards the centre-line of this arm of the alidade. The scale of Babylonian hours is marked 'Hor? [Sun] occasus' and increases linearly from 2 to 12 starting from centre to point third way from tip of the alidade, is divided by 1, subdivided by 1/2 on fiducial edge, and is numbered by 1 with the numbers right-justified against the principal division and their baseline oriented towards centre-line of this arm of the alidade.

Thus concludes the description of the scales on the astrolabe. It remains to consider the engraving style on the instrument, construction details, and the matter of the signature.

There can be little doubt that the engraving on the astrolabe is in the same hand throughout, including on the back of the rete. Although the hand is the same, three distinct styles or 'scripts' are discernible: a mixed-case italic, used for the vast majority of the lettering; an uppercase semi-italic, used for the names of the signs of the zodiac on the ecliptic, the names and numbers of the months in the zodiacal-calendar on the back, the labelling of the shadow scale, the cardinal points, and the hours on the front; and a much more upright mixed-case script used only for the label 'Quadratum Nauticum'.

The letter forms in the mixed-case italic, which is very fluid and very elegant in the most part, generally show very little variation amongst themselves, although those on the back of the rete are slightly freer in form. The variation that does exist is in the length, direction and exuberance of the letter swashes. These vary in form from the restrained to the profuse and there are often significant inconsistencies between the swashes in the same letters in identical words of equivalent importance and function: the swashes in the 'T' in 'Tropicus cancri' on either side of the latitude plate are, for example, formed in a completely different manner from each other, and the descender in the capital 'G's in the names of the winds on the quadratum nauticum are variously present or completely absent, with similar variations occurring in the capital 'X's, 'L's, 'M's and 'R's. While in some cases this variation is clearly due to the desire for a similar decorative effect in different words - on the quadratum nauticum both 'ORIENS' and 'SEPTENTRIO' have similar loops over the beginning of the word, the former extending from the letter 'R' the latter from the letter 'P' - in most cases there is no such clear motive.

While similar variations occur in the style of the swashes in the roman numerals used on the astrolabe, there is little scope for differences in the forms of the arabic numerals. These differ only in their relative sizes, and then only to a limited extent between the two extremes of the numbers for the hours on the tropics in the universal projection and the star magnitudes in the smallest labels for the stars on the rete ('Ophiuchi ma: dex: 4' and 'Orio: dex: hume: [Mars] 1').

All the circular elements of the arabic numerals - the '0', the loop of the '6', the loop of the '9', and the two loops of the '8' - are (indisputably) formed with a punch (including where they occur in the numerals on the back of the rete), as are the circular elements in the symbols for the signs of the zodiac - the loops in [Taurus] and in [Capricorn] and the two loops in [Cancer] - unlike the circular elements of the letters, including the letter 'o', lower and uppercase, which are engraved freehand. (The single possible exception to this rule is the loop of the '6' in the date '1565' in the signature.) Where there is variation between the size of different sets of numerals this has necessitated the use of a punch of a different size.

There is one peculiarity in the form of the arabic numerals: the existence of a variant numeral '4'. In the majority of '4's on the instrument the vertical stroke ends with two easily discernible serifs, as might be expected, probably formed by the addition of a separate short horizontal stroke to the bottom of the vertical stroke. In the minority of '4's on the instrument, and the minority is a large one with a total of ten variant '4's in all, the serifs are absent. Instead of serifs the vertical stroke of the '4' extends below the imagined baseline, curving sharply to the left as it does so. This variation may seem minor as described, but in appearance is quite marked.

The variant '4's occur throughout the astrolabe: in the quadratum nauticum, the hours on the tropic of capricorn in the universal projection, in the numbering of the almucantars and azimuths on both sides of the plate, and in the shadow scale on the limb. The variant '4' is know to occur in other astrolabes from the Arsenius workshop, including on the astrolabe at the Mus?e des arts et m?tiers in Paris signed 'Rennerus Arsenius'. Any further correlation between the presence of variant '4's and the signature 'Regnerus Arsenius' has yet to be established.

Elsewhere on the astrolabe the engraving is not as flawlessly executed as might appear at first sight, several mistakes occurring and rather crude attempts made to correct them. The mistakes include: the number '330' corrected to '130' on the degree scale on the limb; the letters 'ta' inserted in superscript in the word 'Occidentalior' in the label 'Longitudo minor aut Occidentalior' on the quadratum nauticum; the letter 'g' engraved instead of 'q' in the label 'Xaloque mediojorno' on the quadratum nauticum; the abbreviation '?quinoctia:' engraved initially as '?quinoita:' on the 51? plate; the second minim of 'u' and the 's' of 'capricornus' very crudely scored-out to form 'Tropicus capricorni' on the 51? plate; the first letter 'r' inserted as an afterthought in 'Tropicus cancri' on the 45? plate; the second 'e' squashed between the 'M' and the 'r' in the label 'Declina: Meridionalis' on the alidade; 'Hydrae clara' spelt as 'Hydre clara', 'Lanx boreae clarior' spelt as 'Lanx boree clarior', the second 'e' and the planetary temperaments [Jupiter] and [Venus] in 'Persei lat' dex' and the planetary temperament [Venus] below the first colon of 'Andro: [obar]bili:' added as afterthoughts on the rete; 'Horizon obliguus' spelt thus on both sides of the latitude plate; and the punched circular portion of the symbol [Taurus] for Taurus in the ecliptic line on the universal projection omitted completely.

It might also be noted here that both sights on the alidade are placed so as to obscure some letters for the labels of the scales, the letters 'is' in 'Declina: Meridionalis' at one end of the alidade, the letter 's' in 'Hor? occasus' at the other (a design oversight, as it were).

Like the engraving, the materials used in the manufacture of the astrolabe are not flawless. The throne has a small hole in the casting on the front near the centre of its base and a larger one on the back beneath the hooves of the female satyr: flaws which must always have existed. The mater bears a crack 15? clockwise of the throne touching the inside rim of the limb and extending at a tangent approximately 12 mm. The strapwork of the rete has fractured 7 mm from the left tip of the tulip motif in the vicinity of the star named 'Sinister hume{rus}'. This damage to the mater and rete is presumably the result of damage sustained subsequently to their manufacture. The back of the rete is somewhat darkened due also, presumably, to wearing, this time of the gilded surface. The slight rounding of the corners of the strapwork by the beginning of the label 'Corui ala dextra' and at the end of the label 'Cor [Scorpio] [Mars] [Jupiter] 2', along with the proximity of the top of the 'C' in 'Corui' to the edge of the strap, suggests that this edge of the rete has been filed to enable it to rotate freely, although the engraving of the letters in other star-names in the body of the rete is also perilously close to the edge of the straps. The rete is also somewhat worn at this point and at others towards is circumference where the alidade has rubbed over it.

The rete bears two plugs in the strapwork, visible more clearly on the back than the front, by star 40, 'Cauda Cygni' and by 'Ala Pegasi', whose number is obscured by the plug, suggesting it was inserted after the back of the rete was laid out. The reason for these plugs is not clear, whether to fill holes made deliberately or holes made accidentally. Plugs are also to be found on the rim of the limb, precisely at the east and west points. These plug holes that do not extend to the inside rim of the limb but that were clearly made deliberately, perhaps for securing the limb in some way during fabrication. The plugs are accompanied by small circular punch marks in the surface, perhaps suggesting some sort of locating device or clamp.

The wing-nut which screws onto the bolt of the astrolabe is plugged in one place, similarly to the other plugs on the instrument but this time not as skilfully. While the wing-nut and the bolt are congruent in appearance with the rest of the instrument, especially in the character of the gilding, they are presumably later replacements for the originals: the original nut would presumably have been placed on the front of the astrolabe rather than the back, and the original bolt was presumably structurally part of a now-lost regula. To add to the slightly perplexing untampered-with appearance of the instrument in its current state, the present bolt has a locating pin on the underside of its head which mates with a small hole near the centre of the alidade; a hole which does not give the appearance of being a later addition or show any signs of having necessitated re-gilding.

To return to the sights for a moment: these have rectangular pins on their undersides which locate with rectangular holes on the alidade, the hole and pin for one sight being placed asymmetrically of the centre-line of the arm, thus ensuring that the sights are not exchangeable. In addition, one sight and its screw is marked with three dots, the other with a single dot. The reason for these precautions presumably concerns accuracy of alignment of the sights, as well as the fact that the sighting holes in the sights themselves are hemispherically countersunk on one side: the inner side for one sight, the outer side for the other.

While plugs have been used in the astrolabe in a cosmetic function, elsewhere similarly-formed rivets have been used structurally. The limb of the mater is joined to the back-plate of the mater with in excess of 46 rivets. The rivets extend to, and are filed flush with, both front and back surfaces of the astrolabe, and are just visible through the gilding, more so on the back than the front. It is difficult to ascertain to what extend these rivets follow a regular scheme of placement, but they appear, with a few exceptions, to be placed in pairs, alternating roughly along two separate concentric circles which divide the width of the limb approximately equally.

Four plugs or rivets, two large and two small, are also visible, placed within 70 mm of the centre of the astrolabe, passing though the front of the mater to the back and aligned in a straight line running north-east to south-west when viewed from the front. The purpose of these plugs or rivets is unclear. The front of the mater itself is significantly convex towards the centre, but this appears to be formed by simple bending of the plate rather than bulking with the addition of metal (which might necessitate rivets to hold it in place), since the back of the astrolabe is also slightly concave. Whether there is any difference in the radius of curvature of these two surfaces is difficult to ascertain. The purpose of this convexity appears to be to ensure that the single latitude plate of the astrolabe sits, at its circumference, exactly the depth of the rete below the face of the limb (the depth of the inner rim of the limb being greater than the combined depth of the rete and the latitude plate). The top surface of the rete thus sits flush with the face of the limb and the ends of the alidade moves smoothly over the face of the limb.

With this arrangement in operation, it is difficult to see, if as Gunther states (on what evidence is unknown) the astrolabe is missing two plates, how these plates could be stored below the visible plate and yet the rete still rotate freely and flush with the face of the limb with the alidade moving over it, unless the astrolabe previously lacked the convexity towards the centre of the mater. The current concave state of the back means, however, that a regula, cursor and brachiolus could not function satisfactorily (unless they were similarly curved). This peculiarity is perplexing since the concave state of the back does not give any suggestion of being an alteration made subsequently to the rest of the astrolabe, or at least if it was, was a very early modification indeed. Were the concavity original then the astrolabe is never likely to have been supplied with regula, cursor and brachiolus, which would also explain the closeness in style of the current pin and wing-nut to the rest of the instrument. The unlikelihood of the astrolabe being supplied originally without a regula, cursor and brachiolus, together with the coherent stylistic characteristics of the alterations, suggests that they must have been made at a very early stage in the astrolabes history, perhaps contemporary with the possible loss of two plates as referred to by Gunther.

The signature on the astrolabe is placed directly under the throne and reads 'Regnerus Arsenius Nepos Gemm? Frisy fecit Louany anno 1565'. The figure '6' in '1565' is engraved in a smaller size than the other figures, having the appearance of a superscript character and suggesting it was engraved subsequently to the other three figures. This initially somewhat alarming peculiarity in the engraving of the date is not unusual in Arsenius astrolabes.

The engraving style of the signature is in the semi-italic mixed case hand found throughout the instrument, characterised by moderately extended but comparatively restrained swashes on the first letters of the principal words. The hand is indistinguishable from that of the signature on other Arsenius astrolabes of the 1560s, including those signed 'Nepos Gemm? Frisius' alone and those 'Gualterus Arsenius Nepos Gemm? Frisius'. The little that is presently known about workshop practices in sixteenth-century Louvain allows few conclusions to be drawn from the similarity of the engraver's hand, since there is no evidence to determine whether a single instrument was made by a single craftsman or was the result of collaborative effort (and therefore whether the name in the signature is the name of the engraver or of some other person with responsibility for overseeing, initiating or financing its manufacture).

The question remains: is the 'Regnerus Arsenius' named in the signature of this astrolabe to be identified as one and the same person as Gualterus Arsenius? Despite assertions to the contrary elsewhere (see, for example Epact 68941), whether Regnerus Arsenius is one and the same person as Gualterus Arsenius has yet to be conclusively proven either way, either by recent or much older research.

Several arguments have been put forward in support of the idea that Regnerus Arsenius is the same person as Gualterus Arsenius. It is argued that Regnerus was the family name of Gualterus Arsenius, as it was of Gemma Frisius, Gualterus's uncle; that in using the name Regnerus, Gualterus Arsenius was invoking deliberate reference to his illustrious uncle; that the hand of the engraving on instruments signed 'Gualterus' is indistinguishable from the hand of the engraving on instruments signed 'Regnerus'; that Gualterus is referred to by Lodovico Guicciardini, in the first, 1567 edition, of his Descrittione di tuiit I Paesi Bassi, as ' Gualteri Renerio maestro eccelente d'ogno strumento da Mathematica ...'; that surviving letters from Benito Arias Montano, together with the posthumous 1556 edition of Gemma Frisius's De Astroabio Catholico, refer to Gualterus Arsenius in the singular; that the dates of construction of instruments by Gualterus and Regnerus overlap; and that an astrolabe survives signed both with 'Nepos Gemme Frisij faciebat Louany an??1557?' and the monogram 'GAR'.

The suggestion that Gualterus and Regnerus Arsenius were one and the same person seems to originate with Henri Michel in or shortly before 1952, the date of his typescript catalogue of Flemish instrument makers. It is from him that several of the arguments outlined above derive. Under 'ARSENIUS, Rennerus' Michel states that: 'A few instruments, absolutely identical with those of Walter Arsenius, bear this signature. It seems that Rennerus was not different from Walter, and that Renner would be the real family name. Gemma Frisius' name was actually Gemma Regneri (Gemma, son of Regnier, or of the Renner family)'.

Before these assertions by Michel, it had been presumed that Gualterus and Regnerus were distinct but related individuals, probably brothers: Fernand van Ortroy, for example, in his 1911 biography of Gemma Frisius and his relations, stated that: 'Nous admettons que Gauthier, Regnier et Remi ?taient fr?res;', 'Remi' being a possible third brother (Bio-bibliographie de Gemma Frisius, p. 99).

As far as the strength of the arguments that Regnerus is the same person as Gualterus are concerned: it can certainly not be doubted that Regnerus was part of the name of Gemma Frisius - Gemma is referred to in contemporary accounts as 'Gemma Regneri Frisius medicus', 'Gemma Frisius, sive Reinerus Gemma', 'Gemma Reyneri, dictus Gemma Frisius', and 'Rainerus Gemma Frisius'. Also, that Regnerus was the name of Gemma's father is, according to van Ortroy, indisputable: 'd?s lors Regnier ?tait inscontestablement le nom du p?rer, et il faut lire dans le privil?ge susindiqu? 'Gemma, fils de Regnier, m?decin, natif de la Frise'.' (van Ortroy, p. 11).

However, whether Regnerus was part of Gualterus Arsenius's name is more difficult to prove. It is know that Gualterus was the 'nepos' of Gemma, although the intended meaning of 'nepos' may be 'intellectual nephew' as much as 'nephew' by virtue of being Gemma's brother's son. If Gualterus was Gemma's true nephew, would this make this family name 'Regnerus'? If Gemma was the 'son of Regnerus' would his nephew also be a 'son of Regnerus', or a 'grandson of Regnerus'? Did Gemma's own son, Cornelius Gemma ever refer to himself as 'Cornelius Regnerus' or 'Regnerus Gemma'? If not, why not? Such questions are difficult to answer.

The most concrete piece of evidence that 'Regnerus' was part of Gualterus's name comes in the form of the quotation from Lodovico Guicciardini's Descrittione di tuiit I Paesi Bassi, in which he writes: 'Ultimamente metteremo Gualteri Renerio maestro eccelente d'ogno strumento da Mathematica ...' (quoted in Michel, s.v. 'ARSENIUS, Gualterus'). The evidence of the monogram 'GAR' might also be added to this, if it is interpreted as 'Guaterus Arsenius Regneri', but it could equally well, as Koenraad van Cleempoel has pointed out, stand for 'Gualterus ARsenius', if indeed it is the monogram of a maker at all, and not the owner of the instrument.

Even if Gualterus's full name is Gualterus Regnerus Arsenius, this still does not prove that Regnerus Arsenius did not exist in his own rught: Regnerus's full name might have been Regnerus Gualterus Arsenius, the order of forenames in the Arsenius family being alternated among brothers or, indeed, between father and son.

The argument that Gualterus is referred to in the singular in Montano's correspondence and in De Astrolabio Catholico is also of little weight: few would deny that Gualterus Arsenius was one person, whether or not Gualterus and Regnerus were two, so it might be expected that he is referred to in the singular. The argument that the dates of construction of Regnerus and Gualterus astrolabes overlap is similarly ambiguous: it could equally well be argued that Gualterus's normal output of instruments was being supplemented by instruments made by Regnerus in the years for which we have both Gualterus and Regnerus instruments, especially since the number of Arsenius-workshop astrolabes that come down to us from years in which astrolabes signed by Regnerus exist is significantly greater than for other years. (It has in fact been suggested that Adrianus Descroliers assisted in the Arsenius workshop, supplementing the normal output of instruments in the later years of Gualterus's life.)

The argument that Gualterus was bolstering the reference to Gemma by using the name 'Regnerus' is also of little efficacy: did Gualterus really need this more obscure reference in addition to his usual, more explicit 'Nepos Gemm? Frisius' assertion? If he did, why did he not chose to use 'Regnerus' on all his astrolabes, rather than just a small minority, and why did he not employ the two names 'Gualterus' and 'Regnerus' in combination to form 'Gualterus Regnerus Arsenius', instead of only ever using one or the other?

The most striking and troublesome characteristic of astrolabes signed 'Regnerus Arsenius' is certainly the indistinguishable character of the engraving from that on Gulaterus instruments. This remains, however, inconclusive evidence that Gualterus and Regnerus are the same person. Whether or not it is assumed that the engraver of the instrument was the person who signed it (and, as has been mentioned, given the lack of information about workshop practices in sixteenth-century Louvain this can not be taken for granted) the indistinguishable nature of the engraving does not prove Regnerus did not exist of his own accord since the hand of the engraving on the astrolabe of 1573 in the National Martime Museum, London signed 'Ferdinand Arsenius' is also indistinguishable from that on instruments by Gualterus, yet there can be no doubt that Ferdinand Arsenius existed in his own right (since, among other things, he was alive and working until at least 1618).

In contrary to the rather convoluted arguments required to support the idea that Gualterus and Regnerus were the same person, the reason for believing that Gualterus and Regnerus were distinct people is quite simple: four astrolabes survive signed explicitly with the name Regnerus Arsenius. These astrolabes are: the astrolabe under discussion now; an astrolabe signed 'REGNERVS ARSENIVS NEPOS GEMM? FRISY FECIT LOVANY 1565' in the Museum of the Spalding Gentlemen's Society, unique amongst the Arsenius oeuvre in being signed in uppercase; an astrolabe signed 'Renerus Arscenius Nepos Gemm? Frisy Faciebat Louany 1566' in the Museo di Storia della Fisica in Padua, unique amongst the Arsenius oeuvre in having plates and a rete which extend beyond the tropic of capricorn; and an astrolabe signed 'Rennerus Arsenius Nepos Gemm? Frisy Louany fecit 1569' in the Muse? National des Techniques in Paris.

[In terms of numbers, these four astrolabes stand next to 18 instruments signed explicitly 'Gualterus' (plus six if one admits the initials 'GAR', 'G.A.' and 'GAL', which occur once (on an astrolabe of 1557), twice (on an astrolabe of 1568 and astronomical ring dial of 1572), and thrice (on an astrolabe of 1561, armillary sphere of 1562, and cross-staff of 1563) respectively). This compares with four instruments (one armillary sphere of 1568, two astronomical ring dials of 1561 and 1567, and one cross-staff of 1571) signed in the form 'Nepos Gemm? Frisius' without any further initials or name, one instrument signed 'Nepotes Gemm? Frisy' (a theodolite of 1579, six years after the earliest surviving instrument by Ferdinand Arsenius), and slightly less than a douzen unsigned and undated instruments.]

That the four astrolabes signed Regnerus can be put forward as material evidence that Regnerus was not the same person as Gualterus is due in part to the fact that there are few, if any, instances of other contemporary makers signing themselves with different names on different instruments. Instances can certainly be found of makers signing themselves with variants of their name, but rarely with different names entirely. It is also difficult to understand why a maker would chose to do this, especially if that maker already had a reputation established under the other name.

The four astrolabes are not the only material evidence in support of the fact that Regnerus was not the same person as Gualterus. Further evidence comes in the form of references to Regnerus in the account books and correspondence of the Antwerp printer Christopher Plantin. Plantin bought instruments from the Arsenius workshop, recording each of his purchases in a ledger. The name Gualterus Arsenius appears at least once in this context, but so does the name Regnerus Arsenius: on 20th May 1565, Plantin writes 'Pay? un astrolabe a Reynerus Arsenius fl. 25 st. 4'. This is, of course, the date on the astrolabe currently under consideration, but it is impossible to prove if this is one and the same as the instrument to which Plantin is referring.

Those who support the idea that Regnerus is the same person as Gualterus will always find arguments to explain away the distinct and separate references to Gualterus and Regnerus made by Plantin. Plantin might, they argue, have used the names Regnerus and Gualterus interchangeably or he might have written down the name in the account book as it appeared on the astrolabe that he was buying at the time. However, such ad hoc arguments start to wear thin the more often they need to be invoked.

With the possibility of such ad hoc arguments being put forward on both sides, the question might be raised as to exactly what would be required to settle the argument either way. The theodolite of 1579 signed in the plural 'Nepotes Gemm? Frisy Louany fecerunt' has already been mentioned as being inconclusive, due to the acknowledge existence on all sides of Ferdinand Arsenius. Similarly, an instrument signed 'Gualterus Regnerus Arsenius fecit' would also be inconclusive, for reasons already stated. It is difficult to imagine the existence of an instrument signed 'Gualterus Arsenius et Regnerus Arsenius fecerunt', but if the astrolabes signed 'Regnerus Arsenius' and references in the Plantin accounts are to be dismissed, such a signature might well be the only means of conclusively proving that Regnerus Arsenius and Gualterus Arsenius were separate and individual, if not very distinct, instrument makers.

See K. van Cleempoel, et al, Instrumentos Cientificos del Siglo XVI: la Corte Espa?ola y la Escuela de Lovaina (Madrid, 1997); G. M. H[udson], "Sphere No. 7: A Plansipheric Astrolabe by Regnerus Arsenius?", Sph?ra: The Newsletter of the Museum of the History of Science, Oxford, Issue no. 7 (Spring,1998), p. 7; F. van Ortroy, Bio-bibliographie de Gemma Frisius (Brussels, 1920, 'pr?sent? ? la Classe des lettres de l'Acad?mie royale de Belgique, dans sa s?ance du 4 d?cembre 1911); H. Michel, Michel's Makers List, Dec. 2, 1952 (Typescript in possession of the Museum of the History of Science, Oxford); A. S. Osley, A Monograph on the Lettering of Maps etc. (London, 1969); E. Zinner. Deutsche und Niederl?ndische astronomische Instrumente des 11. bis 18. Jahrhunderts (Munich, 1957); and R. T. Gunther, The Astrolabes of the World (2 vols, Oxford, 1932), vol. 2, pp. 384-6.

Giles Hudson

Museum of the History of Science, Oxford
Inventory number 53558

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