Abdal Rahman al-Khazini was a Muslim of Greek origin who was brought to Merv as a slave by the Seljuk king after his victory over the Byzantine Emperor.
His master, al-Khazini, gave him his name and the best possible education in mathematics, philosophy, science and astronomy. Al-Khazini was also a pupil of the famous Persian poet and mathematician Omar KhayyÃ¡m (d 1131 CE) who was living in Merv at that time. Very little is known about his life, but it is known that he was a man who refused rewards and handout sent to him by the wife of the emir.
He preferred to live a simple life on a meager income which he earned himself. The exact date of his death is also not known, but it is believed that he died by the middle of 12th century.
Al-Khazini was a great physicist, astronomer, mathematician, philosopher and an alchemist. He is better known for his contributions to physics.
His treatise; Kitab Mizan al-Hikma (The Book of Balance of Wisdom) written in four volumes, remained an important part of physics among the Muslim scientists. The first volume deals with his predecessorâ€™s theories of centers of gravity, including al-Biruni, al-Razi and Omar Khayam. In this book al-Khazini draws attention to the Greek philosopherâ€™s failure to differentiate clearly between force, mass and weight. He explains how the weight of the air and its density decrease with altitude. By looking at his predecessorâ€™s science, al-Khazini provides crucial records of their contributions that could have remained unknown or lost.
The remaining treatises deal with hydrostatics, most particularly the determination of specific gravities. Al-Khazini goes to extreme lengths in describing the equipment necessary to obtain accurate results. He was very careful in the preparation of his equipment and materials while doing his experiment.
He carried out various experiments with his balances with rigorous attention to scientific accuracy. His interest to determine the specific gravities of precious metals and alloys had some commercial purposes in mind. With the accurate value of specific gravity he could determine the purity of gold and silver without any chemical treatment. To determine the specific gravity of a substance, its weight has to be known in air and water, and the volume of air and water displaced, so most researchers used water balances in their experiments.
Using the same instruments Al-Khazini made repeated experiment with several metals and gemstones. He also measured the specific gravities of many other substances like salt, clay, liquids and amber–a total of fifty one substances.
He developed his own hydrostatic balance, and specialized balances which was extremely precise. He could find the weight of an object on the microgram level, a precision only surpassed in the 20th century.
In another experiment, he discovered that the density of water is greater nearer the earthâ€™s center, which was proved by Roger Bacon two centuries later. Al-Khazini defines heaviness in traditional terms, he says in his book;
â€œA heavy body is one which is moved by an inherent force, constantly, towards the center of the world. I mean that a heavy body is one which has a force moving it towards the central point, and constantly in the direction of the center, without being moved by that force in any different direction; and that the force referred to is inherent in the bodyâ€
It appears that what al-Khazini meant by gravity, is both an idea similar to the modern concept of gravitational potential energy. In any case, al-Khazini appears to have been the first to propose that the gravity of a body varies with its distance from the center of the Earth. In his first sense of the word gravity, the concept was not considered again, till five centuries later by Isaac Newton.
Al-Khazini contributions in astronomy includes a astronomical treatise Zij as-Sanjari or â€˜Sinjaric Tablesâ€™. In this treatise he gave a description of his construction of a 24 hour water clock designed for astronomical purposes which he invented. This was an early example of an astronomical clock. He computed the positions of 46 stars for the year (1115-16 CE). and tables for the observation of celestial bodies at the latitude of Merv. His astronomical treatise was translated into Greek and was studied in the Byzantine Empire.
Al-Khaziniâ€™s book Risala fiâ€™l-alat (Treatise on Instruments) consisted of seven chapters in which he has described about a number of highly specialized and innovative mechanical devices. These instruments include dioptra, (a classical surveying instrument) triangular instruments, triquetrum, (an instrument to find altitude of heavenly bodies) quadrant, sextant and the astrolabe.
Al Khazini, no doubt was a great physicist and astronomer of the middle age who made tremendous advancement in the field of physics and instrument-making. Charles Jillispe, editor of the Dictionary of Scientific Bibliography proclaimed him the greatest of any time.