John Fillmore HayfordBorn 19 May 1868; died 10 Mar 1925 at age 56.American civil engineer and geodesist who established the modern science of geodesy, and made a precise determination of the ellipsoidal shape and size of the earth (1909). The International Union of Geodesy and Geophysics adopted Hayford's calculations in 1924. This International ellipsoid has a flattening of exactly 1 part in 297. The Earth's equatorial radius is 6,378,388 m. The radius along the polar axis is then 1/297 less than that or 6,356,912 m. (Surprisingly, the U.S. did not adopt this datum.) Hayford's theory of isostasy gave that the pressure exerted by the earth's crust is approximately the same over the entire globe, regardless of the nature of the surface (for example, lowlands or mountains). With modification, this theory is now used to explain phenomena within the crust. At the time of his death he was investigating the problems connected with evaporation and the water level of the Great Lakes. |
