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Gunner's Folding Rule
Signed by Humfrey Cole
Dated 1575; London
Brass; 188 mm in length

This rule can only be used at variable angles up to 90?, since a folding skeleton square fixed to the inside of the limbs prevents it from being unfolded further. It consists of two foldable limbs hollowed on the inside to accomodate a folding square and four tablets (two in each limb) engraved on all sides. One limb has folding sights on the outside edge.

Side A

Both edges are divided to provide scales for equal parts for use with maps as follows: 7 parts, divided to 1/7; 54 parts, divided to 1/2, 1/6, 1/18, 1/54; 44 parts, divided to 1/2, 1/22, 1/44; 42 parts, divided to 1/3, 1/21, 1/42; 30 parts, divided to 1/3, 1/15, 1/30; 13 parts, divided to 1/13; 64 parts, divided to 1/2, 1/4, 1/8, 1/16, 1/32, 1/64; 24 parts, divided to 1/2, 1/6, 1/12, 1/24; 40 parts, divided to 1/2, 1/10, 1/20, 1/40; 36 parts, divided to 1/3, 1/9, 1/18, 1/36; 28 parts, divided to 1/2, 1/4, 1/28; 27 parts, 1/3, 1/9, 1/27; 51 parts, divided to 1/17, 1/51; 38 parts, divided to 1/19, 1/38; 46 parts, divided to 1/23, 1/46; 58 parts, divided to 1/29, 1/58; 62 parts, divided to 1/31, 1/62; 33 parts, divided to 1/11, 1/33; 34 parts, divided to 1/17, 1/34; 35 parts, divided to 1/7, 1/35; 39 parts, divided to 1/13, 1/39; 26 parts, 1/13, 1/26; 45 parts, 1/15; 1/45; 50 parts, divided to 1/10, 1/50. The field for 34 is also inscribed with a 'B'.

The apex is inscribed 'Timber and ynches of platt measure withe manye other vses'.

A quarter of the circular joint is inscribed with a 90? scale, numbered by 10 and divided to 2. This scale is used with the movable arm as an index to indicate the angle of separation of the limbs.

Near the ends of the limbs the positions of four stars are given; the inscriptions are now rather worn. The values in the first column seem to indicate the position of the sun when it has the same declination as the listed star, the second column lists the right ascensions of the listed stars (in brackets the modern identifications): 'Pleyad<us>', '7 [Cancer]', '50 [[eta] Tauri]', '{Al}gomey{sa}', '15 [Aries]', '109 [[alpha] Canis Minoris]', 'Arctur<us>', '11 [Gemini]', '20 [[alpha] Bo?tes]', 'Aquila 19 [Aries]', '29 [[alpha] Aquilae]'.

The signature and date 'H C?le 1575' are engraved on the outside edge of the right arm with the two folding sights. Next to them is the inscription: 'The haightes and waightes of Ordenance'. This refers to scales on side B.

Side B

The sections of the right and left limbs closer to the joint are inscribed with tables used in gunnery.

On the left limb is a table with entries for the type of cannon, its weight and the diameter of the barrel. This is continued on the right limb with a table for the diameter of the bullet in inches, the powder needed for every shot in pound, the distance where the bullet first hits the ground in scores by paces (here mathematical paces i.e. one pace equals 5 feet), and the weight of every bullet in pounds.

Further out from the table on the right limb is a text concerning the conversion of length and area measures as follows: '3 Barly cornes to an ynche. 12 ynches a foote. 3 foote a yarde. 5 yardes and 1/2 a pearche. 40 pearches in lengthe and 4 in breadthe an acre. So an acre conteynethe 160 pearches. the halfe acre 80 pearches. a roode 40 pearches'. This text is supplemented by a table giving different side lengths of an acre in perches. This table is also to be found on the three mentioned rules.

Further out on the left arm is a scale for timber measurement in feet, inches and fractions of inches. It is marked 'Square ynches of the timber'. The 'partes' scale is rather worn.

The circular joint is inscribed with the dates of the entry of the sun into a particular sign. The sun is represented by its effigy, the signs by their symbols. The English names of the months are given in abbreviation. It is marked 'The entrauue of ye so<n>ne in the 12 signes'. The column for the months is labelled 'MONTT', the days as 'DAII', the sun as 'SON' and the signes as 'SIG'.

The following dates can be read off: '11 January Aquarius', '10 February Pisces', '11 March Aries', '11 April Taurus', '12 Mai Gemini', '12 June Cancer', '14 July Leo', '14 August Virgo', '14 September Libra', '14 October Scorpio', '13 November Sagittarius', '12 December Capricorn'.

When the limbs are completely opened a folding quadrate is fully spread. On the upper side it is inscribed with a double degree scale 0 to 90 , 0 to 90, numbered by 10 and divided to 5, 1 and 1/5.

The underside has a shadow scale inscribed 'Latus Vmbrae Rectae' and Latus Vmbrae Versae' with two different scales: one 0 to 12, numbered by 3, and the other 0 to 60, numbered by 5 and divided to 1 and 1/3.

Four leaves inscribed on both sides can be folded out from the hollowed part of the limbs when the limbs are fully spread. The all have one little hole at the far end to facilitate opening them out.

They are described as follows: 1 to 2) Left hand upper leaf aide a and b; 3 to 4) Left hand lower leaf side a and b; 5 to 6) Right hand lower leaf side a and b; 7 to 8) Right hand upper leaf side a and b.

1 to 6 have a table for the solar altitude for every 30? for the hours 'ANTE MER' and 'POST MERI', i.e. for every hour of the day. The zodiacal signs are represented by their symbols and are given in the following in abbreviations. There are also small strokes after the values which may stand for fractions, but have not been deciphered. Cole obviously confused the table for Aries and Libra with the one for Cancer and Gemini and just repeated the values given there, so that the values for Aries and Libra are missing.

The right-hand side of leaf 5 is engraved with the right ascensions of five named stars as follows in brackets the modern identifications): 'Scheder 41/2 [[alpha] Cassiopeiae]', 'Ras Algol 41 [[alpha] Persei]', 'Alhayot 711/2 [[alpha] Aurigae]', 'Wega 274 [[alpha] Lyrae]', 'Benanaz 203 [[eta] Ursae Maioris].

Leaves seven and eight are marked with a table for the entry of the sun into a particular zodiacal sign and the right ascension of the beginning of each zodiacal sign measured from the first point of Aries along the equator.

The signs are represented by their symbols. The dates given are all one day earlier than in the table described above except for June, which is identical, and the dates for January and February which are two days earlier. The following values can be read off: '10 March Aries 0', '10 April Taurus 28', '11 May Gemini 57', '12 June Cancer 90', '13 July Leo 122', '13 August Virgo 152', '13 September Libra 180', '13 October Scorpio 207', '12 November Sagittarius 37 [recte: 237]', '11 December Capricorn 270', '9 January Aquarius 302', '8 February Pisces 332'.

The instrument was purchased in 1912 and is described and illustrated in R. T. Gunther, "The Great Astrolabe and other Scientific Instruments of Humphrey Cole", Archaeologia, 76 (1927), pp. 273-317, esp. pp. 296-8; F. A. B. Ward, A Catalogue of European Scientific Instruments in the Department of Medieval and Later Antiquities of the British Museum (London, 1981), p. 105, no. 310; S. Ackermann, Humphrey Cole: Mint, Measurement and Maps in Elizabethan England (London, 1998), pp. 78--80, no. 21.

Silke Ackermann

British Museum, London
Registration no. MLA 1912,11-1.1

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