230 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1957 



Capt. O. S. Eeading, a recently retired photogrammetrist of the Sur- 

 vey, developed a 9-lens mapping camera particularly adapted to the 

 survey of coastal areas. From a height of 14,000 feet, it can snap 

 all the details in 121 square miles of land — a tremendous aid in the 

 incidental problem of shore mapping, notwithstanding the intricate 

 processes of photointerpretation, rectification, and compilation. 



The 1,200 triangulation stations originally laid down by Hassler 

 were forerunners of a vast structure of geodetic control surveys of 

 the utmost importance in all areas of engineering and natural- 

 resource development. Bache started the eastern oblique arc of pri- 

 mary triangulation destined eventually to reach from the Bay of 

 Fundy to New Orleans. This, and the later great transcontinental 

 arc across 2,500 miles of varied terrain from coast to coast, have 

 figured in scientifically important investigations into the most basic 

 and fundamental properties of the earth itself. 



Widespread improvements in the fieldwork methods of astron- 

 omy and geodesy have been highlighted by such dramatic innova- 

 tions as the use of the electric telegraph in 1848 for the determina- 

 tion of longitude between land stations, and B ache's apparatus for 

 measuring a 7-mile baseline with an uncertainty of only one inch. 

 Baseline work, first done with iced measuring bars placed end to 

 end, later employed tapes made of metals that do not change length 

 with varying temperature. Such improvements culminated in the 

 precision that permitted the triangulation of the distance between 

 two California mountain peaks used by Michelson in his classic 

 determination of the speed of light — a distance fixed with a residual 

 probable error of less than one part in five million. Geodetic sur- 

 vey work has seen innumerable smaller improvements, including light 

 and portable theodolites, heliotropes, and electric signal lamps to pin- 

 point signal points at great distances, and the Bilby steel towers, 

 portable and far faster to use than wooden ones, for the elevation 

 of instruments above surrounding objects. New methods of distance 

 measurement directly by radio or light-beam methods are under test 

 now and provide possibilities of superseding time-honored methods 

 of triangulation. 



As a necessary corollary to the involved reductions of geodetic 

 computations, gravity investigations were started in 1875, using 

 Bessel pendulums, later supplanted by temperature-insensitive invar 

 pendulums and the present improved apparatus. Such investiga- 

 tions led to earth-crustal studies by later geodesists John Hayford 

 and William Bowie, who became authors of the fundamental theory 

 of isostasy upon which modern notions of mountain building and 

 other tectonic processes are based. Capt. Bowie, one of the out- 

 standing modern scientists of the Survey, was a strong advocate of 

 comprehensive national mapping programs. He had much to do with 



