vi LIST OF ILLUSTRATIONS 



TEXT-FIGURES 



FIGURE 



1. Key chart to show the positions of five special charts, plates 13, 14A, 14B, 15, 16, of areas in the 



Pacific 25 



2. Distribution of larger deep-focus earthquakes in recent years 43 



3. Tracks of chief vessels on which magnetic observations were made in the Indian Ocean, 1839- 



1916 51 



4. Longitudinal distribution of proportion of amiual change (AH/H) of horizontal intensity 52 



5. Latitudinal distribution of proportion of annual change {AH/H) of horizontal intensity 52 



6. Variation with longitude of AH/H (animal change averaged without regard to sign), of the dis- 



tribution of the proportion of land and water areas, and of secular-change activity approxi- 

 mately determined by the density of the distribution of isoporic lines 53 



7. Distribution of foci of rapid annual change of the magnetic declination, inclination, and horizontal 



intensity, approximate epoch 1920-1925 54 



8. Showing oceanic areas (shaded) between parallels of 60° north and south latitude for which secular 



variation of magnetic elements could not be controlled by land stations on continents and 



islands 55 



9. Navy-Geophysical Union Gravity Expedition 1936-37 67 



10. Chart showing the gravimetric stations occupied by the Italian submarine Vettor Pisani 68 



