Abstract
UNDER the direction of the United States Hydrographic Office, Lieut.-Commander F. M. Green, U.S.N., and the officers under his command, have during the last four years been engaged in determining exactly secondary meridians of longitude by means of the submarine telegraph cables in the West Indies and South America. The result of the West India work in 1874, 1875, and 1876 was the determining the latitude and longitude of a large number of points in the West Indies with the utmost possible exactness; and during the past year this work, of the greatest ralue to geographical and geodetical science, has been continued by making a chain of telegraphic measurements from the Royal Observatory at Lisbon, by way of Madeira, St. Vincent, Pernambuco, Bahia, Rio de Janeiro, and Monte-Video to Buenos Ayres, there connecting with the observatories of Cordova and Santiago. This chain is perfect, with the exception of one link on the coast of Brazil, where the cable was broken, necessitating the procuring of new cable from England; but its completion will be effected before the computation of the observations already made can be finished. The method used for determining the latitude was in all cases that of the zenith telescope, brought to great perfection by the United States Engineers and the Coast Survey; that for differences of longitude, the comparison by repeated telegraphic signals of two chronometers at the ends of the telegraph cable, determining their errors both before and after the comparison by numerous transits of stars over the meridian. All that is needed to make the work of the last year perfect and complete is the telegraphic determination ol the differences of longitude between the Greenwich and Lisbon observatories, and the completion of the imperfect link on the Brazilian coast, both of which will be done during the coming year. Until the observations have been carefully discussed, the results as compared with former determinations cannot be known exactly, but a preliminary computation indicates that the longitude of the coast of Brazil is laid down about three or three and a half miles too far west, this westerly error being indicated in a less degree in the longitudes of Madeira and St. Vincent.
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Geographical Notes . Nature 19, 222–223 (1879). https://doi.org/10.1038/019222a0
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DOI: https://doi.org/10.1038/019222a0