Islamic Civilization

The Rich (Open) Field of Islamic Physics

McGrew notes how, in ‘contemporary usage, the word ‘physics’ denotes an autonomous and highly specialised branch of science which deals with the behaviour of non living systems, bringing them under the scope of the most general natural laws.[1] There was no parallel to this discipline in medieval Islam; yet from the 8^th century onwards there was a profusion of translations, commentaries and learned writings on topics which would today fall under the broad heading of physics.[2] One of the early Islamic scholars who classified sciences, Al-Farabi (874-950), included amongst his works a Book of High Reasoning on Elements of the Science of Physics (Kitab maqalat al-Rafi’a fi usul ilm al-tabia,) a treatise on Vacuum (Kalam fi’l Khala,) a work on optics, and the Great Book of Music (Kitab al-Musiqa al-Kabir).[3] More subjects are integrated within Islamic ‘physics,’ which, as succinctly summarised by Djebbar, includes in its various branches, statics, dynamics, and optical geometry, to which must be added what the Muslims call Ilm al-Hayal (ingenious devices) (seen above under technology).[4] Mc Grew also points out that Islamic scholars wrote profusely on the nature of matter, causality, the theory and practice of mechanics and dynamics.[5] Djebbar also refers to Al-Biruni  Maqala fi n-nisab etc (Treatise on the Relation that Exists Between Metals and Precious Stones); Al-Khayyam: Rissalla fi’l-ihtiyyal… (Treatise on the Process for the Determination of the Weight of Gold and Silver in a Body Made of Both); and of course the better known (and more studied): Al-Khazini’s (d. 1123): Kitab Mizan  al-Hikma (The Balance of Wisdom).[6]

The last mentioned subject, the balance, attracted much of the interest of Muslim writings. This, according to De Vaux, somehow forms ‘a special science'.[7] It is included in Al-Farabi’s classification of sciences, and in Hadji Khalifa’s study of weights from the medical perspective.[8] The Banu Musa brothers, Qusta Ibn Luqqa, and Ibn al-Haytham all wrote on the Roman balance of unequal arms: The Kariston. In the first half of 11^th century, the Syrian Elias bar Shinaya wrote a treatise on the balance dealing with coins, weights, and measures, and explaining the use of various kinds of scales.[9]

Two of the earliest, and most interesting treatises on the subject are by Thabit Ibn Qura (d.901): kitab fi sifat al-wazn wa ikhtilafihi (Book on the Properties of Weight and non Equilibrium) and kitab fi'l qarastun (Book on Beam Balance), which deal with mechanics primarily.[10] Gerard of Cremona translated this work into Latin  in the 12^th century under the title Liber carastonis. Until 1911, there existed three manuscripts of it, one at Berlin’s Stadtbibliotheq, another at the Jesuit library in Beirut and the third at the India  Office in London (MS. 767, VII, fols 198-208).[11] The first two have been lost. The work by Thabit on the Balance brings to attention the sharp contrast in approach to the subject between Greeks and Muslims. Mc Grew notes that one of the simplest mechanical devices, the lever, had been investigated mathematically by Archimedes, who gave an elegant proof that the forces required to keep the unequal arms of a lever in balance were inversely proportionate to the length of the arms. In the course of his proof, Archimedes assumed that two equal weights located at different points on one arm of the lever produced the same effect as if they were both located at the midpoint between them-an assumption which is intuitively plausible but for which he gave no rigorous justification, whilst Thabit provides an intriguing argument for this assumption in his Kitab al-Qarastun (Book of the Balance).[12]

The subject of tides also attracted a wide focus of Muslim writers from the earliest times, the Muslims insisting on the correlation existing between the phenomenon of high and low tide and the course of the moon.[13] They became familiar with this, and the explanation given of it in the 9^th century by Abu al-Ma’ashar (Albumazar) in his ‘Introductorium magnum ad Astronomiam', according to Duhem (by no means a fervent admirer of things Islamic), remained a classic throughout the Middle Ages.[14] Al-Kindi and al-Biruni pursued this tradition, the latter explaining that the increase and decrease in the height of the ebbs and tides occurred in cycles on the basis of changes in the phases of the moon. He gives a very vivid description of the tide at Somnath, and traces the latter's etymology to the moon.[15]

Magnetism also attracted early Muslim scientists including among them Jabir Ibn Hayyan (8^th-9^th century). The magnetic compass was soon widely used by Muslims for navigation purposes.[16] Wiedemann has early in the 20^th century made studies of the subject.[17] More recently, Schmidl wrote a very good article on the use of the magnetic compass in the Islamic world, focusing on two previously unpublished works, the first by the Yemeni Sultan al Ashraf (ca. 1290) and the second by the astronomer Ibn Sim'un (ca. 1300) of Cairo . This lengthy article includes a brief introduction of the history of the magnetic compass in Europe and China  and mentions previously known early Islamic sources on the instrument and its use. This is followed by some remarks on the authors and the manuscripts, the Arabic texts with English translations, and comments on problems the author encountered while working on the texts.[18]

On light and sound, Al-Biruni  concluded that the speed of light was immensely greater than that of sound, whilst works on music by al-Kindi include notions for the determination of pitch.[19] Ibn Sina , who studied motion, contact, force, vacuum, and heat also studied light and musical theory. He suggested amongst others that light was capable of being measured, whilst on music he studied the physics of musical tones and of harmony.[20] He dealt with doubling with the octave and doubling with the fourth and fifth, decisive steps towards the harmonic system.[21] Among secondary sources dealing with this particular subject, nothing matches Farmer’s countless works completed during the first half of the 20^th century, examining the subject from every single perspective.[22] 

Abu Bakr al-Razi, centuries prior to Newton, made distinction between absolute and relative space; absolute space, which is three dimensional and infinite, exists quite independently of the bodies contained in it.[23] On this Pines comments:

‘Al-Razi  appears to suggest as a proof for the existence of three dimensional space the fact that if one removes by means of the estimative faculty, or more probably the imagination (al-wahm), (all existing) bodies, absolute space will still remain in existence, i,e. it will still be imagined by that faculty (wahm).[24] Elsewhere he adduces as a proof for the existence of empty space outside the world the fact that simple folk, whose soul has not lost its spontaneity, state that their reason tells them that such a space exists. In other words, Al Razi considers that the fact that a physical conception or representation is accepted as certain 1) by reason, or 2) by the estimative faculty or the imagination, is a proof of its real existence.’[25]

Ibn Baja’s (Avempace) physics has been explored by Moody, as a result of Moody’s enquiry whether Galileo’s Pisan dynamics had any medieval origin.[26] This led him to the translation of Ibn Rushd’s commentary on Aristotle’s Physics, where he came across Ibn Baja, who was a predecessor of Ibn Rushd. Ibn Baja was criticised by Ibn Rushd, but, when the Christian scholastics, Moody points out, commenced to study Aristotle’s Physics and write their commentaries about it, they became aware of Ibn Baja’s criticism of his law of motion, and had to weigh such criticism with that of Ibn Rushd.[27] It was the positions which these two (Ibn Rushd and Ibn Baja) defended, which had, according to Moody, consequences of a scientific order, for they involved the fundamental issue of whether motion at uniform velocity, against no resistance, is the effect and measure of a force, or whether it is to be defined and measured by the rate at which work is done in changing the kinetic condition of a material body.[28]

It is the practice among Muslim scholars that diverse sciences are associated for determining, or ascertaining results in practice and theory. In this instance, mechanics, for instance, is used to demonstrate the validity of mechanical theories; for example the law of inverse proportions can be demonstrated by showing that the ratio of two weights in equilibrium on a lever is inversely proportional to the ratio of their distance from the fulcrum.[29] Al-Biruni  even used the balance to demonstrate the rules of Jabr and of muqabala, and conversely, al-Khazini used the laws of proportion to determine the accuracy of balances.[30]  

The most decisive contribution of Muslim physics is again in the field of experimentation, a matter which demarcates Islamic science from its predecessors’.[31] Greek physics reasoned and deduced but hardly ever calculated, says Benoit; calculation, he adds, being the essential foundation not only of the sciences but also of technology and economic activity.[32] Hill also views that Aristotle speculative physics, and reverence to him had ‘a stultifying effect upon creative thought.[33] In contrast the experimental path taken by Islamic scientists constituted not just a breakthrough of considerable implication for physical investigations, but also freed scientific thought.[34] Amongst Islamic experimenters in the subject were Al-Biruni  and Al-Khazini, whose experimental skills were obvious in determining specific weights.[35] In order to determine the specific weight of a specimen, its weight has to be known in air and water, and the volume of air and water displaced by the specimen. For this, Al-Biruni used a ‘conical vessel,' and weighted meticulously the substance he wanted to study, then dipped it into his conical instrument that was filled with water. He weighed the water, which had been displaced by the immersed substance and which was escaping the instrument through a hole conveniently placed. The ratio between the weight of the body and that of the same water volume gave the specific weight sought.[36] Al-Biruni summarised his findings in a number of tables, which show how extremely close he was to modern data (some of the deviations to be explained by the impurity of the specimen and by temperature differences in his experiments).[37] His figures for the specific gravities of gold (19.05), mercury (13.74), copper (8.83), iron (7.74), tin (7.15) and lead (11.29) are very close to modern values.[38] Al-Biruni also determined the specific weight of some liquids, and established the differences in the specific weights of hot and cold water and fresh and salt water. Most of all, he was the first to introduce control tests in the practice of experiments.[39]

Finally it is worth citing some secondary sources for the study of Muslim physics. First is Pines, especially in relation to the originality of Islamic science in the field.[40] There is a good, albeit short summary by Winter;[41] as well as Jaouiche’s translation (into French) and added comments of Thabit Ibn Qurra’s Kitab al-Qarastun.[42] Rozhanskaya (in collaboration with I.S. Levinova,) gave a good outline on statics.[43] Hill also made a valuable contribution to the subject.[44] There are also excellent entries in the Dictionary of Scientific Biography on al-Khazini and Thabit Ibn Qurra.[45] The best contributions to the subject remain the much older ones (late 19^th-early 20^th century) such as Khanikoff’s translation of al-Khazini’s work on the balance,[46] and, above all, Wiedemann’s (1852-1928) writings.[47] These, complemented with primary sources, can build a better understanding of Muslim physics.

In this section chapter, the focus is on the Islamic atomic theory, and Al-Khazini’s Balance of Wisdom.