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 APPENDIX 581 and the oreation of the exarchate, with its large powers, decisively reduced the import- ance of the Praetorian Praefect. The importance of this change, as a preparation for the similar changes, in the administration of the Eastern provinces, out of which the later Theme-organization grew, has been brought out by Gelzer, Die Genesis der byzantinischen Themenverfassung (Abhandlungen of the Saxon Gesellschaft der Wissenschaften, vol. 18, 1889), 8-10. For the list of the Exarchs of Italy, see Diehl, Etudes, 173 ; for the succession of the magistri militum and Exarchs, and the Praetorian Praefects of Africa, Diehl, L'AIrique byzantine, 596 sqq. 21. THE COMET OF A.D. 531— (P. 461) The identity of the comet of a.d. 1680 with the comets of a.d. 1106, a.d. 531, B.C. 44, &c, is merely an ingenious speculation of Halley. See his Synopsis of the Astronomy of Comets, at end of Whiston's " Sir Isaac Newton's mathematick Philosophy more easily demonstrated " (1716), p. 440 sqq. The eccentricity of the comet of a.d. 1680 was calculated by Halley (Philosophical Transactions, 1705, p. 1882), and subsequently by Encke, Euler, and others, — on the basis, of course, of the observations of Flamsteed and Cassini. Newton regarded its orbit as parabolio (Principia, 3, Prop. 41) ; but it has been calculated that the eccentrioity arrived at by Enoke, combined with the perihelion distance, would give a period of 8813-9 years (J. C. Houzeau, Vademecum de l'Astronome, 1887, p. 762-3). The observations were probably not sufficiently acourate or numerous to establish whether the orbit was a parabola, or an ellipse with great ecoentricity ; but in any case there is nothing in the data to suggest 575 years, nor have we material for comparison with the earlier comets which Halley proposed to identify. For the Chinese observations to which Gibbon refers, see John Williams, Observations of Comets from Chinese Annals, 1871 : for comet of b.c. 44, p. 9, for a doubtful comet (?) of a.d. 532, p. 33, for comet of a.d. 1106, p. 60. 22. ROMAN LAW IN THE EAST— (C. XLIV.) New light has been thrown on the development of Imperial legislation from Constantine to Justinian, and on the reception of Eoman law in the eastern half of the empire (especially Syria and Egypt), by the investigations of L. Mitteis, in his work " Reichsrecht und Volksrecht in den ostlichen Provinzen des romischen Kaiserreichs " (1891). The study is mainly based on Egyptian papyri and on the Syro-Roman Code of the fifth century, which was edited by Bruns and Sachau (1880). It was only to be expeoted that considerable resistance should be presented to the Roman law, which became obligatory for the whole empire after the issue of the Constitutio Antoniniana (or Law of Caracalla), among races which had old legal systems of their own, like the Greeks, Egyptians, or Jews. The description which Socrates gives of the survival of old customs at Heliopolis, which were contrary to the law of the empire, indicates that this law was not everywhere and absolutely enforced ; the case of Athenais, put off by her brothers with a small portion of the paternal property, points to the survival of the Greek law of inheritance ; and the will of Gregory Nazianzen, drawn up in Greek, proves that the theoretical invalidity of a testament, not drawn up in Latin and containing the prescribed formulae, was not practically applied. Theory and practice were inconsistent. It was found impossible not to modify the application of the Roman principles by national and local customs ; and thus there came to be a particular law in Syria (cp. the Syro- Roman law book) and another in Egypt. The old legal systems of the East, still surviving though submitted to the influence of the Roman system, presently had their effect upon Imperial legislation, and modified the Roman law itself. The influence of Greek ideas on the legislation of Constantine the Great can be clearly traced. 1 It can be seen, for instance, in his law concerning the bona materni generis, 1 Cp. Mitteis, Beilage iii. p. 548 sqq. Ammian calls Constantine novator turbatorque priscarum legum.