THE DOCTRINE OF ISOSTATIC COMPENSATION 715 



the same latitude. 1 If this statement is well founded, it would be 

 difficult to escape the conclusion that at least partial compensation 

 exists for the oceanic areas. But from examination of the figures 

 in Hecker's original monograph, 2 a different form of statement would 

 seem better to express the facts. Up to the time of Hecker's 

 Atlantic voyage geodesists, through basing their conclusions upon 

 pendulum observations made upon a few oceanic islands, had held 

 the belief that gravity is uniformly in excess over the oceans ; and 

 the force of Helmert's statement lay in the fact that it exploded 

 this notion, which had received official sanction from an interna- 

 tional geodetic congress. A better form of statement would appear 

 to have been that Hecker's results did not in general reveal the high 

 excess above normal values which had been expected. But values 

 of Ag. which range from 146 units 3 of defect to 161 units of excess 

 can hardly be called nearly constant unless errors of measurement 

 be assumed to be excessive. 



Hecker's grouping of his data objectionable in that it tends to 

 efface significant local anomalies. — Hecker's paper is open to the 

 objection that by a process of averaging the local significance of 

 Ag. is made largely to disappear. Of this, two examples will 

 suffice: the first, of measurements made over the shallow North 

 Sea and British Channel with depths ranging from 60 to 160 meters 

 only; and the second, a group of four measurements made between 

 the Cape Verde Islands and the equatorial ridge over unknown but 

 presumably large depths, which from a few not very distant sound- 

 ings are probably generally in excess of 5,000 meters (Tables III 

 and IV). 



Hecker's revision of his data after the Black Sea cruise. — The 

 figures as first published by Hecker were shown by Baron Eotvos 

 to need correction for direction of motion of the vessel (west or east) , 

 and after having tested the magnitude of this correction in a special 



1 F. R. Helmert, "Dr. Heckers Bestimmung der Schwerkraft auf dem atlantischen 

 Osean," Sitzungsher. d.k. preuss. Akad. d. Wiss. z. Berlin, I (1902), 126-28. 



2 0. Hecker, "Bestimmung der Schwerkraft auf dem atlantischen Ozean, sowie 

 in Rio de Janeiro, Lissabon und Madrid, Verojjentlichung d. k. preuss. Geod. Inst. 

 (N.F.), No. n (Berlin, 1903), pp. 84-85, PL 6. 



3 Measured in thousandths of a centimeter of acceleration. 



