NO. 8.] REMARKS ON THE EARTH'S CRUST. 73 



element of the surface of the inner nucleus as in the rest of the earth's crust, 

 or, what is almost the same thing, that these parts are also, on an average, 

 in an equilibrium of pressure upon the inner nucleus. If this supposition is 

 correct, we must be able to infer from it the peculiarity that appears to 

 characterise the coast-stations, namely, that the gravity increases a little with 

 an approach towards the coast-margin of the continents. It has been stated 

 above that for 37 coast-stations on various continents, HELMERT found 

 the difference between the observed and the normal acceleration to be 



0-00030 0-00005 m. 



According to PUTNAM, the coast-stations in North America along the Atlantic 

 exhibit positive, or very small negative, differences, while the stations in the 

 interior show much larger negative differences. 1 



The relative determinations made by the Austrian Navy during the years 

 1892 1898, also always give positive differences at the coast-stations examined, 

 these being situated on various continents Australia, Asia, Africa and 

 South America along the Indian, Atlantic and Pacific Oceans. 2 



The incline of submarine parts of the continents towards the ocean depths 

 outside differs in different places. It is generally somewhat less nearest land 

 (about 1 in 250 for a distance of 50 km.), and increases farther out to 

 about 1 in 100. The incline is steeper, however, at several places, e. g. 

 along the west coast of North and South America, where it amounts to 

 1 in 40. 3 



If, as before, Q stands for the density in the firm mass under the oceans, 

 and p! for that under the continents, we may imagine the crust of the earth 

 to be formed of a sea, of depth fe 2 , extending over the whole earth, and resting 

 upon a shell of thickness (h l h%) and a density Q, when we add, as regards 

 the continents, a mass of which the sum total is zero, but distributed in such a 

 manner that above there will be a covering of thickness fo 2 and density 



1 United States Coast and Geodetic Survey, Appendix No. 1. Report for 1894, p. 28. 

 Relative determinations of gravity with half-seconds pendulums, and other pendulum 

 investigations. G. R. PUTNAM. Washington, 1895. 



2 Relative Schwerebestimmungen durch Pendelbeobachtungen. Ausgefflhrt durch die 

 k. und k. Kriegs-Marine in den Jahren 18921894. Herausgegeben vom k. und k. Reichs- 

 Kriegs-Ministerium, Marine-Section. Vienna, 1895. 



Relative Schwerebestimmungen durch Pendelbeobachtungen, Heft II. VerOffent- 

 lichungen des hydrografischen Amtes der k. und k. Kriegs-Marine in Pola. Pola 1898. 



3 F. R. HELMERT. Hohere Oeodasie Bd. II, p. 345. 



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