SECRETARY'S REPORT 159 



sources has led to the following conclusions: 1. The inhomogeneous 

 layer is extended from the top of the mantle to a depth of approxi- 

 mately 100 to 200 km. 2. The isothermal surfaces are not simple 

 geometrical surfaces. Temperatures on a "level surface" near the 

 top mantle have fluctuations with amplitude of about 100° C. 



The Satellite-Tracking Program is now at fruition in its geodetic 

 objectives, not only for the earth's geopotential but also in the area 

 of geodetic positions and the establishment of a much more precise 

 worldwide geodetic system.^ Several independent calculations of im- 

 proved coordinates of the Baker-Nuim stations have been made dur- 

 ing the past year. When all detailed questions in these different 

 approaches to the problems have been resolved, a consolidated, con- 

 sistent result is expected. 



Over 45,000 observations from the 12 Baker-Nunn Stations were 

 analyzed by Dr. George Veis, with the assistance of Mrs. Elizabeth 

 Wombwell, to derive the coordinates of the stations and the absolute 

 deflection of the vertical for seven datums.^ Although these results 

 are preliminary, a value of 6,378,169 meters for the semimajor axis 

 of the earth's ellipsoid is obtained from the above derived deflections. 

 A total of 26,447 precisely reduced photographic observations of 11 

 objects were analyzed by Mr. Izsak to obtain least-squares estimates 

 for the corrections to the coordinates of the 12 camera stations. The 

 latter calculation was made in conjunction with determinations of 

 the coefficients for the tesseral and sectorial harmonics of the 

 geopotential. 



Using simultaneous observations of satellites from pairs of the five 

 Baker-Nunn cameras in the Americas, Dr. Veis and Antanas Girnius 

 have determined the directions of the lines connecting the stations 

 with an accuracy of better than 1 second of arc. More data from 

 simultaneous observations are now under analysis. These will allow 

 the determination of directions in both the North American and the 

 European datums and will permit a connection between them. 

 Dr. Kolinlein also devised several computer programs for the adjust- 

 ment of space triangulations. By using the correlation of already 

 adjusted coordinate values, he combines a pure geometrical method 

 and a dynamical method for a joint adjustment computation of the 

 station coordinates.^ 



Although instrumented satellites are beginning to be important, 

 satellite drag determined from tracking data continues to be the 

 most productive source of information concerning the atmosphere 

 above 200 km. Recent work at the Observatory, made possible by 

 the Injun 3 and Explorer 17 satellites, includes the study of the atmos- 

 phere under conditions of low solar activity and at low heights and 



See footnotes, p. 177. 



