96 LECTURES 



cliain of triangles which stretches along the coast, forming the basis 

 of the survey, and in the astronomical determinations connected with 

 it. It has been demonstrated that, in works of this character, ulti- 

 mate economy is promoted in proportion to the precision with which 

 the work is first executed. There is every demand, therefore, for the 

 most perfect instruments, the most approved methods of observation, 

 and the best practical skill in establishing the true positions of the 

 primary points of the survey. 



The American Coast Survey now represents, according to the best 

 authorities, the most perfect forms of practical science applicable to 

 works of this character ; and a general sketch of the methods era- 

 ployed in the geodetic operations, in order to illustrate the value of 

 the new measurements of arcs of the earth's surface which will follow 

 the completion of the primary chain of triangles along the coast, will 

 not be out of place in connexion with this subject. 



The triangulation of the Atlantic and Gulf coasts when completed 

 will extend diagonally through 19 degrees of latitude and 30 degrees 

 of longitude. The extreme points of this triangulation will be dis- 

 tant from each other, by the general line of the coast, nearly 3,000 

 miles ; the chain of triangles extending from the eastern boundary of 

 Maine to the western boundary of Texas. It will probably be many 

 years, perhaps centuries, before this triangulation will be extended 

 across the continent to the Pacific ocean ; but, ultimately, this will 

 undoubtedly come to pass ; in the mean while the survey of the 

 western coast of our territory is progressing according to the plan 

 followed on the eastern coast. 



The triangulation of the eastern coast is now continuous from 

 Mount Desert, in Maine, to Shalotte inlet, south of Cape Fear, in 

 North Carolina ; stretching over more than ten degrees of latitude 

 and as many degrees of longitude, including the coast of ten States, 

 and the greater part of the coast of two others ; then, with an interval 

 of about seventy miles, it extends along the coast of South Carolina 

 and Georgia. 



Large detached portions of the triangulation of the coast of Florida, 

 Alabama, Mississippi, Louisiana, and Texas have been completed, and 

 a few years only will be necessary to fill the intervals so as to make a 

 continuous chain from the eastern boundary of Maine to the western 

 boundary of Texas. 



This triangulation will rest upon ten or twelve principal base lines, 

 measured on different parts of the coast, which afford the double pur- 

 pose of starting the work at nearly the same time at different points, 

 and for ultimate verification of its accuracy. 



The accuracy of the work has been tested by the connexion of several 

 of these bases in the progress of the survey, and the degree of precision 

 attained is so remarkable as to justify a somewhat detailed description 

 of the various processes by which aerial distances of many miles length, 

 and hundreds of miles from the starting point, or base, may be deter- 

 mined by the wonderful applications of geodesy, with but a few inches 

 of probable or possible error. 



When it is said that a certain part of this triangulation is completed, 

 it is meant that all the mechanical work in the field for measuring the 

 base lines and the angles, and for determining the latitudes and longi- 



