حجر الفلاسفة
Book Four, "The Alchemist", takes place in Samarkand, in the 17th century. An alchemist named Khalid attempts to fool the Khan into believing that he has discovered the Philosopher's stone, but his fraud is uncovered and his hand is chopped off as punishment. Khalid becomes depressed and disenchanted with alchemy and decides to destroy all his Alchemical books. His friend Iwang (a Tibetan Buddhist mathematician) and son-in-law Bahram (a Sufi blacksmith) instead convince him to test the veracity of the claims in the books and thus see if there is any true wisdom to be gained. They devote themselves to practical demonstrations and experiments that greatly improve knowledge of various aspects of physics, chemistry, mathematics, biology, and weaponry, and in the process create the scientific method. Their discoveries create interest (and alarm) amongst the religious madrasahs of the city, many of whom also go along with the new fashion of building and testing scientific apparatuses. But most of all, they catch the eye of the Khan's powerful advisor, who sees in their inventions the possibility of great military technology, to fight the rising Chinese threat to the East.