THE DOCTRINE OF ISOSTATIC COMPENSATION 703 



that the lines of equal anomaly of gravity have been drawn for 

 each millimeter of acceleration. 1 The sharp changes — steep 

 gradients — upon the map thus come into prominence, and these 

 show very close correspondence with strong abnormality of the 

 magnetic forces and with the intensity of earthquakes, the seismicity 

 of the province having been investigated by Rethly. 2 



For the area of the North German plain, Deecke, making use 

 of data upon magnetic constants determined by Schiick and of 

 those of gravity issued by Helmert from the Royal Prussian 

 Geodetic Institute at Potsdam, has shown that the lines of equal 

 anomaly of gravity correspond closely with those of terrestrial 

 magnetism (involving both inclination and declination), and that 

 these lines are further, in many cases, those of recent faulting, 

 and in some cases were probably the seats of movement during 

 the earthquake of October 23, 1904. 3 In this connection it is of 

 interest that a resurvey of magnetic elements in Japan subsequent 

 to the great earthquake of 189 1 indicated remarkable changes in 

 the isomagnetics of the province. 4 



In connection with a general survey of geodetic data assembled 

 from many regions, Helmert, though approving Hayford's views, 

 has concluded that gravity values are in many localities not com- 

 pletely in harmony with Pratt's hypothesis, 5 and that this is espe- 

 cially true for the oceanic islands, for the margins of the continental 



1 Baron Roland Eotvos, "Bestimmung der Gradienten der Schwerkraft und ihrer 

 Niveauflachen mit Hiilfe der Drehwage," Abh. der XV. Allgemeinen Konferenz der 

 Erdmessung in Budapest, 1906, I, 1-59 (reprint). See also, by the same author, 

 " Uber Arbeiten mit der Drehwage ausgefiihrt im Auftrage der koniglichen ungarischen 

 Regierung in den Jahren 1909-1911," Bericht an die XVII. Allgemeine Konferenz der 

 Intemationalen Erdmessung (Budapest, 1912), pp. 1-17. 



2 Foldrajzi Kozlemenyek, XXXIX, 391-420. 



3 W. Deecke, "Erdmagnetismus und Schwere in ihrem Zusammenhange mit dem 

 geologischen Bau von Pommern and dessen Nachbargebieten," Neues Jahrb. /. 

 Mineral., etc., Beilage Bd. 22 (1906), pp. 114-38, Pis. 1-3. 



4 D. Kikuchi, Jour. Coll. Sci. Univ. Tokyo, V, 149-92. 



5 Wenn Pratts Hypothese erfiillt ist, so miissen sich die Schwerestorungen Ag. 

 lediglich aus Hohenstorungen der Massenlagerung iiber der Ausgleichsflache erklaren 

 lassen. Dies gelingt aber nicht vollig; man muss daher auch noch Horizontalver- 

 schiebungen annehmen, welche die Massenlagerung gestort haben. Es treten sogar 

 ausgedehnte Massenstorungen auf, wo die sich gegenseitig ausgleichenden Massen 

 nicht erkennbar sind, so dass man nur schlechthin von Anhaufungen und Defekten 

 sprechen kann, die sich also als erhebliche Abweichungen von Pratts Hypothese 

 darstellen" {Sitzungsber. Berliner A kad. d. Wiss. [II, 1908], 1060). 



