Telegraphic Determinations of Longitude. 5 
reliance was placed were decidedly in error. The result from the 
chronometric expedition in 1855 previously referred to differing 
over a second of time. 
In constructing charts for use at sea, the accurate determination 
of latitude and longitude is of the utmost importance. The 
navigator starting on a voyage must know the exact position of 
his destination as well as the location of dangers to be avoided. 
He must know the error and rate of his chronometer when he 
sets out, but as the rate is not constant he should have some 
means of re-rating it at any place where he may stop. If the 
longitude of this place is well determined, the operation of 
obtaining the error and rate is an easy one, and may save his 
vessel from loss. ; 
Surveys, of coasts or countries must have well established 
starting points, and while the latitude of a place is comparatively 
easy to determine, the longitude, except when the telegraphic 
method is used, is attended with more or less uncertainty. 
In 1873, Commodore R. H. Wyman, U. 8. N. Hydrographer to 
the Bureau of Navigation, organized by permission of the Navy 
Department, an expedition for the telegraphic determination of 
longitude in the West Indies and Central America. The sub- 
marine cables of the West India and Panama Telegraph Co. had 
just been completed, extending from Key West through Havana 
and Santiago de Cuba, south to Jamaica and Aspinwall, and east 
through the Virgin and Windward Islands to the northeast coast 
of South America, thus affording admirable facilities for the accu- 
rate determination of many points. It had long been known that 
the longitudes of various points in the West Indies and in Central 
and South America, did not harmonize, there having been no 
systematic attempt to determine them with relation to each other 
or to a common base. Longitudes in, the western part of the 
Caribbean Sea depended upon the position of the Morro light- 
house at Havana, which had been determined by occultations. 
Further to the eastward, positions depended upon that of Fort 
Christian at St. Thomas. This in its turn depended upon the 
observatory of Major Lang in the Island of Santa Cruz about 
forty miles distant. This position depended upon numerous 
observations of moon culminations and occultations. Martinique 
and Guadeloupe in the Windward Islands had been surveyed by 
French officers who based their positions upon longitudes derived 
from moon culminations. The absolute determination of these 
starting points would of course fix all points derived from them. 
