Graphic Methods in Nautical Astronomy

Abstract

IN the issue of NATURE published on October 24 last (vol. cii., p. 155), there appeared an account of an ingenious chart devised by Mr. G. W. Littlehales, of the United States Hydrographic Department, for dealing rapidly with certain problems in nautical astronomy which involve the solution of a spherical triangle when the three sides, or the two sides and the included angle, are known. The article is entitled “A New Graphic Method in Nautical Astronomy,” but it would appear that the idea has been, familiar in France for more than, five-and-twenty years. The possibility of constructing a chart like that made by Mr. G. W. Littlehales, was demonstrated by Maurice d'Ocagne so long ago as 1891 in his work “Nomographic: les calculs usuels effectués au moyen des abaques,” p. 84, and an abacus devised by him on these lines was described in W. Dyck's “Katalog mathematischer und mathematisch-physikalischer Modelle, Apparate und Instrumente,” published in 1892, p. 163. A figure of the chart can be found in a paper by d'Ocagne which appeared in the Journal de l'Ecole Polytechnique (second series, 4th cahier, 1899, p. 224), and also in his “Traité de Nomographie,” 1899, p. 328. In a modified form the chart was employed by E. Collignon in 1898 (see his “Note sur la détermination de l'heure du passage du soleil dans un plan vertical,” Journal de l'Ecole Polytechnique, loc. cit., pp. 123–35).