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Published online by Cambridge University Press: 18 January 2010
This paper discusses navigation tables based on the decomposition of the astronomical triangle into two right-angled spherical triangles by a great circle arc extending from the zenith to the meridian of an observed celestial body. In a recent fairly comprehensive study of some thirty short-method tables in which the division of the PZX-triangle forms the principle of construction, nineteen are of the species to be discussed.
Following the introduction in 1871 of the first short-method table by Thomson, some twenty years were to pass before any real advance was made in this field. Thomson's table was in fact re-issued by Kortazzi in 1880 and by Collet in 1891, in modified forms, but it was Professor F. Souillagouët of France who is to be credited for introducing something novel and decidedly better than Thomson's table. Unlike the earlier ones it was designed specifically for the Marcq Saint Hilaire method of sight reduction and, in contrast to Thomson's table which was based on the division of the PZX-triangle by a perpendicular from X, Souillagouët's was based on division by a perpendicular from Z.