The first two great lights that appeared were Al-Chindus, and Geber who discovered the red oxide and bichloride of mercury, nitric acid, hydrochloric acid, and nitrate of silver. Geber’s _Summa Perfectionis_ and _Liber Philisophorum_ embody his researches on the purification and malleability of metals. In the ninth century, the Arab alchemist Rhazes flourished. In his great work entitled _El Hharvi_, he alludes to realgar, orpiment, borax, mixtures of sulphur and iron with copper, and of mercury with acids, and arsenic. He further recommends physicians to use alcoholic preparations and animal oils, etc. He states: “The secret art of chemistry is nearer possible than impossible; the mysteries do not reveal themselves except by force of labour and perseverance. But what a triumph it is when man can raise a corner of the veil which conceals the works of God!” The knowledge displayed of chemistry and its application to the arts at that early period is wonderful, but books were few. The chief evidence of this knowledge is exhibited in the many specimens and art monuments in the museums of Spain, showing the skill of the Saracens and of the Moors. A little later Mesué states, “certain principles had been recognised as to the analytical classification of the bodies which compose organic matter”. Of the ancient necromancers who have figured in history and romance, Merlin was perhaps the most extraordinary. The earliest mention of his name is in records of the eleventh century, although he appears to have flourished about the time of the Saxon invasion of Britain, in the latter part of the fifth century. He is first mentioned in connection with the fortune of Vortigern, who is represented by Geoffrey of Monmouth, as at that time King of England. Vortigern having lost all his strongholds in his struggle with the Saxons, at length consulted his magicians as to how he was to defend himself from his troublesome foe. They advised him to build an impregnable tower, and chose a suitable site for its erection. The builders set to work with might and main, but were astonished to find, that as fast as they built in one day, the next morning the earth had swallowed it up, and not a vestige remained. So the king called the wise men together again, when they arrived at the conclusion that the only way to remedy the matter was to cement the walls of the tower with the blood of a human being who was born of no human father.