NO. 8.] REMARKS ON THE EARTH'S CRUST. 81 



America, and ^ = 2'66, we obtain for the increase in the acceleration which 



this force will produce, 



0-46 mm. 



The effect will probably be somewhat greater if the incline is supposed 

 to be rather less; for very gentle inclines, the effect will, as previously men- 

 tioned, again decrease. 



For points farther in on the continent, the increase in the acceleration, 

 on account of the slope, will take place rather more slowly as we approach 

 the coast-line, than if the continent were cut off abruptly, as the slope will 

 act very much as an extension of the continent seawards. In other respects, 

 the course of the phenomenon will be on the whole as we have shown it above. 

 We thus se ethat upon the above-mentioned supposition concerning the compo- 

 sition of the earth's crust, it is easy to explain the fact that gravity generally in- 

 creases somewhat on an approach to the coast-margin. Our deduction, however, 

 leads moreover to a result with which we have hitherto been unacquainted. 

 If we imagined ourselves going out to sea from the coast-margin, we found, 

 in the case of the continent falling abruptly off towards the bottom of the ocean, 

 that the acceleration out at sea will prove to be about as much diminished as it 

 was increased at the same distance landwards. If we take into consideration 

 the more or less steep incline of the continents towards the ocean depths, it 

 must still appear, as we go out farther from the coast, that the acceleration 

 first decreases and falls below the normal, and then once more rises and 

 approaches it farther out from land. The change upon land and out at sea, 

 however, will no longer take place almost symmetrically in relation to the 

 coast-line, as the slope of the negative land-masses by which, in the case of 

 the sea, we can replace the continent in question, is in an opposite direction 

 to that of the latter, since both land-masses together are to form a continuous 

 shell all over the earth. 



The Fram expedition has been the first to give information as to what 

 are the circumstances with regard to gravity out on the ocean. We have 

 seen that the gravity is normal over the Polar Basin. As already mentioned, the 

 irregular, trembling motion in which the ice-masses might possibly have been 

 during the observations, would only cause a shortening of the period of the pen- 

 dulum employed, so that we may assume that the values found for the ac- 

 celeration have not come out too small. In spite of this, however, one obser- 



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