Islamic Civilization

Instruments [1]

 The use of instruments made it possible to reach precise calculations, and also resolve first hand astronomical problems. Precision, from the early stages of Islamic civilisation occupying the highest concern of Islamic scholars. Thabit Ibn Qurra (b.826), for instance, stated that pure Greek reasoning cannot always match observation in accuracy, declaring ‘What is perceived by sense does not lend itself to such precision.'[2] His own treatise on sundial theory contains all the necessary mathematical theory for the construction of sundials in any plane.[3] Such instruments resolved what were hitherto complicated or insoluble problems. The quadrant, for instance, of which are three varieties, such as the sine quadrant were described by al-Khwarizmi, was widely used throughout the Islamic world to solve problems of spherical astronomy for any latitude.[4] These instruments varied from the handy astrolabe to the very bulky ones used in observatories.

The astrolabe is one of the earliest instruments the Muslims developed and perfected. It is a flat and circular instrument, with, in the centre, a disc engraved with indicator lines whose positions are worked out mathematically; the disc rotating in a holder, one side of which has a fret of thin pieces of brass ending in points that represented the stars.[5] By rotating the inner disc it is possible to find rising and setting times for the celestial bodies, and to determine the occurrence of other astronomical events, which hence makes the astrolabe a graphical computer.[6] For Williams, the astrolabe was the most important astronomical calculating device before the invention of digital computers, and the most important astronomical observational device before the invention of the telescope.[7] The oldest astrolabe in the History of Science Museum at Oxford was made about 950.[8]

The uses of the astrolabe seem limitless.[9] Al-Khwarizmi  claimed that the astrolabe could solve 43 problems, whilst Al-Sufi claimed that with it he could answer a thousand astronomical questions.[10] Within the limits of their definitions of problems and questions, Saunders points out, both were probably correct.[11] Thanks to the astrolabe, it was possible to calculate the altitude and azimuth of the sun, the moon, stars and planets; time; and to measure distances and heights.[12] The astrolabe was used in astronomy, of course, but also in other areas such as surveying, navigation, and so on.[13] Some such other usages will be touched upon as this work progresses.  Extremely precise, it was capable of measuring the altitude of the sun or the stars to an accuracy of about one degree.[14] An instrument of this kind, Pedersen explains had never been at the disposal of Latin  astronomers,[15] and once it was introduced in Europe (very likely the early 11^th century, though its first known use dates from later in the century, with Walcher of Malvern),[16] it made it possible to measure celestial phenomena, and express them very accurately.[17]

Krisciunas elaborates on an astronomical use of the astrolabe.  He explains that the sighting device, usually to be found on the back of the astrolabe, is called the alidade, from the Arabic al-idadah (turning radius). It is a straight edge which points to degree markings around the edge while it turns about the centre of the astrolabe. The alidade has a sight at each end made up of a flat piece of metal with a small hole (about 2mm) drilled through. One hangs the instrument from a finger of one hand and rotates the alidade until one can sight a known star through the two holes. In the case of the sun one would cast the round image of the sun through the top hole on to the lower sighting hole. One then simply reads off the elevation angle from the outside edge of the back of the astrolabe. Then, on the front of the astrolabe, one rotates the rete to place the star or Sun at the correct elevation angle in the eastern or western half of the climate. It is then possible to determine the elevation angles and azimuths of all the other stars represented in the rete (without any calculating whatsoever), determine the local sideral time (the right ascension corresponding to the meridian), or to determine the local solar time. Then, using one’s known geographical longitude and a graph of the equation of time (the difference between mean and apparent solar time) it is possible to derive the modern standard time (e.g Greenwich Mean Time).[18]

Muslim makers of astrolabes have attracted the attention of Mayer, who described over a hundred of them, their works, the places and date the astrolabes were made, and gives a first class bibliography as well.[19] Mayer also gives the present locations of such astrolabes, and when appropriate, their owners. Because astrolabes were the first scientific instruments in history, sophisticated and elegantly presented, he points out, it makes access to them very difficult. These astrolabes are dispersed all over the world. Ibrahim B. Sa’id  (fl 11^th century) of Valencia  constructed many astrolabes, one of which being part of a Spanish collection, is now in the Lewis Evans Collection in the Museum of the History of Science, Oxford; another can be found in the Museo Astronomico, Rome, (N 688), and a few more scattered elsewhere.[20] Amongst those made by Mohammad b. Fattuh of Seville  (early 13^th), is an azaphea (safiha) now in the Osservatorio Astronomico Rome (no 694ii); another in the Bibliotheque Nationale, Paris, and another in the Adler Planetarium, Chicago.[21] An astrolabe built by Abu Bakr B. Yusuf Marrakech  (13^th century) is now at the observatory of Strasbourg; another was once held in a Dominican monastery in Toulouse, and another was in the possession of Baron de Larrey. One of the earliest astrolabes still extant was made by Khalif in the 9^th century. It was formerly at the Landau collection, Paris, before it was moved to the Billmeir collection in London.[22] Even earlier than Khalif was Ahmad b. Khalaf, who made an astrolabe for Caliph Ja’far b. Muktafi Billah, formerly in the Barbier collection, then moved to the Bibliotheque Nationale, Paris.[23]

Makers of astrolabes frequently wrote on the subject, too. Al-Zarqali of Toledo , (b.1029) wrote al-Safiha al-Zarqaliya (Azafea), a treatise on the universal astrolabe, invented by him. It was a stereographic projection for the terrestrial equator and could be used to solve problems of spherical astronomy for any latitude.[24] It was derived from the universal astrolabe of al-Shakkaz, and includes a table of 29 stars with ecliptical coordinates intended to be marked on the instrument.[25] Ibn al-Samh (11^th century), who flourished at Grenada , wrote two treatises on the use and construction of the astrolabe, besides compiling astronomical tables.[26] Before him, and most certainly the first Western Muslim to write on the instrument, was Al-Majriti (d.1007) who wrote ‘some chapters indispensable for everyone who wishes to construct an astrolabe,' which includes a table of 21 stars entitled Table of the Places of the Fixed Stars...[27] Al-Farghani’s treatise on the same subject explained the mathematical theory behind the instrument and corrected the faulty geometrical constructions of the central disc that were current then.[28] Al-Badi al-Asturlabi (d. 1140), who at some point was a director of observations in the palace of the Seljuk sultan Mughith al-Din Mahmud, was, according to Sarton, the greatest expert of his time in the knowledge and construction of astrolabes,[29] hence his name. Al-Nairizi (who also compiled astronomical tables) and Qusta ibn Luqqa are two other writers on the subject.[30] Fewer writings on the subject appeared after 13^th century, and they include those by Al-Muwaquit (d.1336),[31] and the Moroccan Al-Jazuli (fl. 1344).[32]

A great number of other astronomical instruments were constructed and written about by Muslims, of which the following is only a brief outline, Sedillot, noted above, providing the best data and sources for the subject. Jabir Ibn Sina n (fl early 9^th century) constructed astronomical instruments.[33] Amongst the instruments that can be cited is the gnomon used for measuring altitudes of the sun and other planets; the celestial sphere to explain celestial movements,  and the sundial for calculating the time of day and the azimuth (compass bearing).[34] Al-Khujandi (d. 1000) constructed an instrument al-Suds al-Fakhri (sixth of a circle) for the measurement of the ecliptic.[35] Al-Khujandi states that with this instrument degrees, minutes and seconds could be measured, whereas before him, instruments did not indicate seconds.[36] For the observation of the planets, al-Khujandi constructed an armillary sphere and other instruments, besides a universal instrument called al-Ala al-Shamila (Comprehensive Instrument), which was used instead of the astrolabe or the quadrant, and that could be used for any latitude.[37] Ibn Baja (b.1106) constructed a planetary system based on eccentric circles but not epicycles,[38] whilst Jabir ibn Aflah (d.1150), already cited for his Turquet, designed a portable celestial sphere to measure and explain the movements of celestial objects.[39] Al-Khazini, (fl 1115), famed for his Balance of Wisdom (more on this further on) described the construction of a 24 h water clock designed for astronomical purposes.[40] More importantly, Al-Khazini is the author of a treatise on instruments Risala fi’l Alat, which has seven parts, each of which was devoted to a different instrument: a triquetrum; a dioptra; a ‘Triangular instrument;’ a quadrant;  devices involving reflection; an astrolabe; and simple aids for the naked eye; the quadrant is in fact called a suds, or sextant, and performs the functions of the sextant, although its arc is 90⁰.[41] Apart from describing the devices and their use, the treatise also demonstrates their geometrical basis.[42] A great number of sundials were made, including  those by Al Mursi (d. 1315),[43] and Ibn Basa (d.1316), who also improved and simplified the Azafea of Al-Zarqali so that it could serve any latitude with a single tablet.[44] Al-Mizi (b.1291)  constructed quadrants and also wrote treatises on their construction, whilst Ibn Sarraj (fl 1325) developed several varieties of markings for the almucantar quadrant, besides devising various highly ingenious trigonometric grids as alternatives to the simple sine quadrant.[45] Ibn al-Majdi (b.1358) wrote Khulasat al-Awqal, which explains the use of the sine quadrant; and Risala fi-l-Amal bi rub al-Muqantarat al-maqtu a treatise on the use of a quadrant bearing projections of almuncatars or parallels of altitude; and also a treatise on sundial theory.[46] Al-Maradini (fl.1400) in Damascus , and later in Cairo , devised a universal quadrant, consisting of two shakkaziya quadrants of the same size attached at their centres, and designed to solve a given problem in spherical astronomy by transferring the problem to a plane stereographic projection of the celestial sphere.[47]

Possibly the last greatest writer/maker of instruments in Islamic civilisation was Al-Kashi. In 1416 he composed the short Risala dar shar ialat I rasd (Treatise on Observational Instruments ) dedicated to the Turkish  sultan Iskander.[48] In this work al-Kashi describes the construction of eight astronomical instruments: Triquetrum; armillary sphere; equinoctial ring; double ring; fakhri sextant, an instrument ‘having azimuth and altitude,’ an instrument ‘having the sine and arrow,’ and a small armillary sphere.[49] At about the same time he completed Nuzha al-Hadaiq (The Garden Excursion), which he further revised upwards in 1426 at Samarkand  (Samarqand).[50] In this work he describes the ‘Plate of Heavens’ an astronomical instrument he invented, and also describes the plate of conjunctions.[51] The first plate (of heavens) is a planetary equatorium and is used for the determination of the ecliptic latitudes and longitudes of planets, their distances from the earth, and their stations and retrogations; like the astrolabe, which it resembles in shape, it was used for measurements and for graphical solutions of problems of planetary motions by means of a kind of monogram; the second instrument is a simple device for performing a linear interpolation.[52] Subsequently, a well known illustration from a 16^th century Ottoman Turkish manuscript, now in Istanbul, shows a large bronze armillary instrument of observation with a supporting frame constructed entirely in wood.[53] As drawn, North observes, the complete instrument would have been nearly five times the height of the men shown using it.[54]

Celestial globes have occupied a leading place in Islamic interest. Amongst their makers are Ibrahim ibn Said al-Wazoon and his son Mohammed, who in 1081 built in Valencia  a metal celestial globe that was 209 mm in diameter, which represented the celestial sphere as given by Ptolemy, but with increases to the longitudes of all the stars; and the names of the constellations in Arabic Kufic characters.[55] Qaysar (1178-1251) born at Asfun, Upper Egypt ; astronomer, mathematician, and engineer, built in 1225 the second oldest existing Arabic celestial globe.[56]  Sarton points out that the five oldest are by the Muslims,[57] and are kept as follows:

1) In Firenze (constructed in Valencia  by al-Sahli in 1080-1).

2) One kept in Naples (constructed in 1225-6 by Qaysar).

3) One kept in London (constructed in 1275/6 by Muhammad b. Hilal  of Mosul.)

4) That of al-Urdi (constructed in 1279 or 1289, kept in Dresden.)

5) A fifth which is not dated, but possibly anterior to one or many of those listed (kept in the Bibliotheque Nationale of Paris.) [58]

Emilie Savage Smith’s work on celestial globes is by far the most instructive of all on the subject.[59] The problem lies with the author’s using the expression ‘Islamicate’ to refer to Islamic, which is quite deprecating of the Islamic role; an attitude constantly reinforced (turning into a rant in places) by assertions such as found in the foreword (p.iv): ‘the production of scientific instruments derived from the Greco Roman tradition in the Islamic world.’ Then, in the first lines of the Abstract (p. ii), she insists again: on the ‘references in classical Greek and Roman literature to earlier globes that are no longer extant.’ Then, again, in page vi of the preface she uses the term: ‘Islamicate instead of Islamic’ because, she argues:

‘It can be used to refer to objects or cultural features that are not directly related to the religion but are often based on traditions taken from other cultures and nurtured and developed by Muslims and non Muslims alike.... These globes represent a tradition of instrument design inherited from the Hellenistic, Roman, and Byzantine worlds..’

To Smith’s insistence on this point, can be counter argued that there is no concrete evidence of any globe from the Greek world. After all, Byzantium only fell in 1453. If the Greeks had made them, they would have been found there. Islamic celestial globes date from centuries earlier than that, and can still be traced. Besides, there is no reference from any witness of Greco-Roman globes in Byzantium, or any other part of the Latin -Greek world. And the Muslims, just as with other objects or works, would have mentioned them had they seen them.  Where Smith is absolutely right, though (p.vi), is the wish to see more celestial globes now in small museums and private collections come to light and be made available for study to help provide a fuller picture of the development of the design and construction techniques.

More importantly, as Savage Smith points out, from early in the 12^th century, probably before 1120, we have a fascinating treatise on ‘the Sphere that rotates by itself’ by Al-Khazini, who later dedicated some other astronomical writings to the Seljuk ruler, Sanjar Ibn Malik (1097 to 1157). This treatise, which has been recently edited and translated (by Lorch in 1980),[60] describes a celestial globe which, instead of being placed in the usual set of rings, is half sunk in a box and propelled so as to rotate once a day by a mechanism of pulleys driven by a weight resting on top of a reservoir of sinking sand.[61] This sphere

‘Is set halfway into a box whose upper surface serves to mark the horizon. Over the sphere, along the north south line, was affixed a half circle of brass, which served as a meridian ring, with the axis of the globe set at the south pole inside the box and the north pole at a hole in the meridian ring corresponding to the geographical latitude of Merw. The rest of the box covered the top of the mechanism, which automatically rotated the sphere one rotation per day. The equator was inscribed on the globe and divided into 360 equal parts. Taking as a pole a point 23 degree 35 minutes measured along the meridian ring from the pole of the equator, the ecliptic was inscribed and divided into zodiacal houses and degrees. Al-Khazini then indicated a circle on the surface of the box around the globe, which he also divided into 360 degrees, and on which he named the four points of the compass, so as to serve as the horizon ring.’[62]

The value of this object can never be overestimated.