[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 11ᵛ-14ᵛ = pp. 31-36. [33] _The Chronicle of Jocelin of Brakelond_ ..., H. E. Butler (ed.), London, 1949, p. 106. [34] C. B. Drover, "A medieval monastic water-clock," _Antiquarian Horology_, 1954, vol. 1, no. 5, pp. 54-58, 63. Because this water clock uses wheels and strikes bells one must reject the evidence of literary reference, such as by Dante, from which the mention of wheels and bells have been taken as positive proof of the existence of mechanical clocks with mechanical escapements. The to-and-fro motion of the mechanical clock escapement is quite an impressive feature, but there seems to be no literary reference to it before the time of de Dondi. [35] _Annales de la Société Royale d'Archéologie de Bruxelles_, 1896, vol. 1/8, pp. 203-215, 404-451. The translation here is cited from Drover, _op. cit._, (footnote 34), p. 56. [36] L. Thorndike, _The sphere of Sacrobosco and its commentators_, Chicago, 1949, pp. 180, 230. [37] The album was published with facsimiles by J. B. A. Lassus, 1858. An English edition with facsimiles of 33 of the 41 folios was published by Rev. Robert Willis, Oxford, 1859. An extensive summary of this section is given, with illustrations, by J. Drummond Robertson, _The evolution of clockwork_, London, 1931, pp. 11-15. [38] M. Jules Quicherat, _Revue Archèologique_, 1849, vol. 6. [39] M. C. Frémont. _Origine de l'horloge à poids_, Paris, 1915. [40] For this, I have used and quoted from the very beautiful edition in English, prepared by Silvanus P. Thompson, London, Chiswick Press, 1902. [41] See E. G. R. Taylor, "The South-pointing needle," _Imago Mundi_, Leiden, 1951, vol. 8, pp. 1-7 (especially pp. 1, 2).