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In 1818 Laplace proposed that the Academie des Sciences in Paris set up a prize to be awarded to whoever succeeded in constructing lunar tables based solely on the law of universal gravity. In 1820 the prize was awarded to Carlini and Plana and Damoiseau by a committee of which Laplace was a member. But Laplace strongly criticized the Carlini-Plana approach to the lunar theory. A dispute ensued that is reconstructed on the basis of hitherto unknown letters exchanged between Carlini-Plana and Laplace, and on the basis of papers published in Connaissance des temps and in Zach's Correspondance. After the exchanges, public and private, between Carlini-Plana and Laplace, the latter concluded that the results of the Italian astronomers and those arrived at by Damoiseau following the method of his Mecanique Celeste were fairly close, and that the purpose of the Academie in establishing the prize had been reasonably fulfilled.

Summary A detailed description of an as yet unrecorded astrolabe quadrant in a private collection is presented. A date between 1291 and 1310 is deduced from the calendrical data engraved on it. The characteristics of the newly recorded instrument have been compared with those of six other medieval astrolabe quadrants. The newly recorded instrument appears to present an early, if not the earliest, stage of development in the history of the astrolabe quadrant. In the comparison the newly recorded instrument is also distinguished by the red and black colours applied to differentiate between the superposed scales of the astrolabe quadrant. The names and the positions of the stars on the instruments were used to establish a connection between two of the instruments studied, those in Rouen and Oxford, and a manuscript tradition on the construction of the astrolabe quadrant, exemplified by MS Oxford Ashmole 1522. The data on three other astrolabe quadrants are shown to stem from star lists in treatises on astrol...

Summary This paper examines the purport of epact tables encountered on scientific instruments, and explains their use. The epact is a valuable chronological aid for calculating the age of the moon. In handbooks of chronology, usually two types of epacts are distinguished: the epact used in medieval times, and the so-called Lilian epact used after 1582 in the Gregorian perpetual calendar. By examining the rules for calculating the age of the moon, it turns out that the Julian and Gregorian epacts encountered on instruments must be distinguished from the medieval and Lilian epacts. It is shown that the Julian epact was already in use in 1478, and that, by adjusting for the shift of ten days in the date of the vernal equinox, the Gregorian epact was derived from it in 1582. The common association of the latter with the Lilian epact employed in the Gregorian perpetual calendar is incorrect. It is further shown that in contrast to the medieval and Lilian epacts, which served purely ecclesiastical purposes, the...