Adelard has been described as “a dim and shadowy figure in the history of European learning,”[28] and the dates of his birth and death are unknown. We possess, however, a number of his works and some may be either approximately or exactly dated. In the preface to his translation of the astronomical tables of Al-Khowarizmi he seems to give the year as 1126.[29] The Pipe Roll for 1130 informs us that Adelard received four shillings and six pence at that time from the sheriff of Wiltshire. This suggests that he was in the employ of the king’s court,[30] and his brief treatise on the astrolabe seems to be dedicated to Prince Henry Plantagenet,[31] later Henry II, and to have been written between 1142 and 1146. It was probably one of his last works and in it he mentions specifically three earlier works.[32] Two other writings, which are the best known and apparently the most original of his works, namely the _Questiones naturales_ and _De eodem et diverso_, may be dated approximately from the fact that they are dedicated respectively to Richard, Bishop of Bayeux from 1107 to 1133, and to William, Bishop of Syracuse, who died in 1115 or 1116. Both works are addressed to Adelard’s nephew, who is presumably the same person in both cases, one in the form of a letter, the other of a conversation, and both justify Adelard’s studies in foreign lands. In an appendix to this chapter the question when these two treatises were written and their relations to each other will be discussed more fully. [Sidenote: Mathematical treatises.] The subjects of a majority of Adelard’s known works and translations are mathematical or astronomical. The most elementary is a treatise on the abacus, _Regule abaci_,[33] in which his chief authorities are Boethius and Gerbert and he seems as yet unacquainted with Arabic mathematics.[34] But most of the mathematical treatises extant under Adelard’s name are from the Arabic, such as his translation of Euclid’s _Elements_;[35] of the astronomical tables of Al-Khowarizmi--who flourished under the patronage of the caliph Al-Mamum (813-833)--“apparently as revised by Maslama at Cordova,” under the title _Liber Ezich_; and, if by a “Master A” Adelard is meant, of a treatise of the first half of the twelfth century on the four arts of the quadrivium and especially on astronomy, which is apparently also a work of Al-Khowarizmi.[36] Some of the introductory books on the quadrivium have been printed,[37] but “the astronomical treatise has not yet been specially studied.”[38] One therefore cannot say how far it may indulge in astrology, but we are told that Adelard translated from the Arabic another “astrological treatise, evidently of Abu Ma’ashar Dja’afar,”[39] or Albumasar. We have already mentioned in another chapter the ascription to Adelard of one Latin translation of the superstitious work of Thebit ben Corat on astrological images, and in the present chapter the treatise on the astrolabe for Henry Plantagenet.