[7] A summary of the content of the manuscript sources, illustrated by the original drawings, has been published by H. Alan Lloyd, _Giovanni de Dondi's horological masterpiece, 1364_, without date or imprint (?Lausanne, 1955), 23 pp. It should be remarked that de Dondi declines to describe the workings of his crown and foliot escapement (though it is well illustrated) saying that this is of the "common" variety and if the reader does not understand such simple things he need not hope to comprehend the complexities of this mighty clock. But this may be bravado to quite a large degree. [8] See, for example, the chronological tables of the 14th century and the later mentions of clocks in E. Zinner, _Aus der Frühzeit der Räderuhr_, Munich, 1954, p. 29 ff. Unfortunately this very complete treatment tends to confuse the factual and legendary sources prior to the clock of de Dondi; it also accepts the very doubtful evidence of the "escapement" drawn by Villard of Honnecourt (see p. 107). An excellent and fully illustrated account of monumental astronomical clocks throughout the world is given by Alfred Ungerer, _Les horloges astronomiques_, Strasbourg, 1931, 514 pp. Available accounts of the development of the planetarium since the middle ages are very brief and especially weak on the early history: Helmut Werner, _From the Aratus globe to the Zeiss planetarium_, Stuttgart, 1957; C. A. Crommelin, "Planetaria, a historical survey," _Antiquarian Horology_, 1955, vol. 1, pp. 70-75. [9] Derek J. Price, "Clockwork before the clock," _Horological Journal_, 1955, vol. 97, p. 810, and 1956, vol. 98, p. 31. [10] For the use of this material I am indebted to my co-authors. I must also acknowledge thanks to the Cambridge University Press, which in the near future will be publishing our monograph, "Heavenly Clockwork." Some of the findings of this paper are included in shorter form as background material for that monograph. A brief account of the discovery of this material has been published by J. Needham, Wang Ling, and Derek J. Price, "Chinese astronomical clockwork," _Nature_, 1956, vol. 177, pp. 600-602. [11] For these translations from classical authors I am indebted to Professor Loren MacKinney and Miss Harriet Lattin, who had collected them for a history, now abandoned, of planetariums. I am grateful for the opportunity of giving them here the mention they deserve. [12] A. G. Drachmann, "The plane astrolabe and the anaphoric clock," _Centaurus_, 1954, vol. 3, pp. 183-189. [13] A fuller description of the anaphoric clock and cognate water-clocks is given by A. G. Drachmann, "Ktesibios, Philon and Heron," _Acta Historica Scientiarum Naturalium et Medicinalium_, Copenhagen, 1948, vol. 4.