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 such an acceleration existed was made in the year 1695 in a paper published in the Philosophical Transactions of the Royal Society, entitled 'Some Account of the Ancient State of the City of Palmyra, with short Remarks upon the Inscriptions found there ', a paper which is at least a monument of its author's versatility. The paper neither measures nor demonstrates the acceleration, but merely indicates Bagdad, Aleppo, and Alexandria as the places in and near which the observations were made by which the Moon's motion was determined, and asks for observations of the phases of lunar eclipses at these places in order to determine their longitudes. He expressed a hope, destined never to be fulfilled, that he would one day demonstrate the existence of an acceleration.

It is curious that this suggestion of Halley's should have evoked no inquiry into the question till Dunthorne took the matter up fifty-four years later. Dunthorne relied wholly on eclipses, and the interest attaching to the question of acceleration has led to many elaborate discussions of ancient and mediaeval eclipses from his time to the present day. Long before Dunthorne's day most of the eclipses mentioned in Greek and Latin writers had been satisfactorily identified and dated, but eclipses have retained their double interest, in which astronomical evidence is brought to the aid of the student of history, and historical evidence is brought to the aid of the student of astronomy. I have treated in papers published by the Royal Astronomical Society the astronomical results that can be derived from ancient eclipses. In this lecture I shall assume the validity of