64 THE FLOOR OF THE OCEAN 



numbers are expressed in milligals, a milligal being again de- 

 fined as practically one millionth of average gravity at the 

 earth's surface. 



On grounds too technical for present description, it appears 

 that at each volcanic mountain a free-air anomaly somewhat 

 exaggerates the implied excess of attracting rock, but in general 

 by less than 50 per cent. A milligal means a force equal to the 



FIGURE 33. ANOMALIES OF GRAVITY IN HAWAII ISLAND. 



