258 SEE— FURTHER RESEARCHES ON [April 24, 



pcndeiicc of moutitain making upon the sea the earth emphatically 

 is not a failing structure. So far from failing by collapse, our 

 planet seems to be expanding from 10 to 100 faster than it con- 

 tracts from loss of heat. Thus have arisen all the highest moun- 

 tains and plateaus of the globe. These great uplifts invariably 

 face the deepest oceans, from which the expulsion of lava has mainly 

 proceeded. Such antiquated doctrines as that the earth is a fail- 

 ing structure are now absolutely without excuse, and practically 

 abandoned, and the sooner they disappear from scientific literature 

 the better for sound knowledge of the physics of the earth. 



§ 51. Changes of the Force of Gravity in Regions Affected by 

 the Movement of Lava Beneath the Crust. — In view of the demon- 

 strated movement of lava streams beneath the crust of the globe, 

 it follows that such bodily displacement of matter but a short dis- 

 tance below the surface may modify sensibly the observed intensity 

 of gravity. A region which is being undermined will have the 

 intensity of gravity decreased, and a region which is being filled 

 up will have the attraction increased. And not only will the in- 

 tensity vary, but also the direction of the vertical, according to the 

 movements which occur beneath the, crust. And these efl^ects may 

 be large enough to become sensible to very refined observation. 



It is in this way that the anomalies of gravity in the neigh- 

 borhood of mountains have arisen in the process of mountain form- 

 ation. And in regions where the expulsion of lava is still in 

 progress, both the direction and intensity of gravity are subject to 

 change by earthquakes. Thus in the region of the Aleutian Islands, 

 the east coast of Japan, and man}- other places, such as the west 

 coast of South America, the direction and intensity of gravity is cer- 

 tainly subject to change by seismic disturbances. 



As the crust of the globe often sufifers horizontal and vertical 

 movement during the greatest earthquakes, the altitude and a.zitn]ith 

 of places are also subject to change; and exact geodetic triangula- 

 tion remains valid only for the interval between great earthquakes. 

 Even then there may be a ver}' slow and gradual settlement owing 

 to plastic yielding of the crust and especially of the substratum 

 beneath. Thus after earthquakes such as occur in Peru and Chili, 

 Japan and Alaska, gravity and geodetic determinations need repeti- 



