[22] Abulcacim Abnacahm, _Libros del saber_, edition by Rico y Sinobas, Madrid, 1866, vol. 3, pp. 241-271. The design of the instrument has been very fully discussed by A. Wegener, "Die astronomischen Werke Alfons X," _Bibliotheca Mathematica_, 1905, pp. 129-189. A more complete discussion of the historical evolution of the equatorium is given in Derek J. Price, _The equatorie of the planetis_, Cambridge (Eng.), 1955, pp. 119-133.
[23] E. Wiedemann, and F. Hauser, "Über die Uhren im Bereich d. islamischen Kultur," _Nova Acta; Abhandlungen der königliche Leopoldinisch-Carolinische Deutsche Akademie der Naturforscher zu Halle_, 1915, vol. 100, no. 5.
[24] E. Wiedemann, and F. Hauser, _Die Uhr des Archimedes und zwei andere Vorrichtungen_, Halle, 1918.
[25] The manuscripts in question are as follows: Gotha, Kat. v. Pertsch. 3, 18, no. 1348; Oxford, Cod. 954; Leiden, Kat. 3, 288, no. 1414, Cod. 499 Warn; and another similar, Kat. 3, 291, no. 1415, Cod. 93 Gol.
[26] H. Schmeller, Beiträge zur Geschichte der Technik in der Antike und bei den Arabern, Erlangen, 1922 (_Abhandlungen zur Geschichte der Naturwissenschaften und der Medizin_ no. 6).
[27] Once more I am indebted to Professor Loren MacKinney and Miss Harriet Lattin (see footnote 11) for making their collections on Gerbert available to me.
[28] Item 198 in Gunther, _op. cit._ (footnote 21). I am grateful to the authorities of that museum for permission to reproduce photographs of this instrument.
[29] Sotheby and Co., London, sale of March 14, 1957, lot 154. The outer rim of the rete has 120 teeth.
[30] The Latin text of the treatise on the Albion, has been transcribed by Rev. H. Salter and published in R. T. Gunther, _Early science in Oxford_, Oxford, 1923, vol. 2, pp. 349-370. An analysis of its design is given in Price, _op. cit._ (footnote 22), pp. 127-130.
[31] Such evidence as there is for the existence and form of the clock is collected by Gunther, _op. cit._ (footnote 30), p. 49.
[32] I have discussed this new manuscript source in "Two medieval texts on astronomical clocks," _Antiquarian Horology_, 1956, vol. 1, no. 10, p. 156. The manuscript in question is ms. 230/116, Gonville and Caius College, Cambridge, folios 11^{ v}-14^{ v} = pp. 31-36.