Open main menu

Littell's Living Age/Volume 132/Issue 1702/Miscellany

The Variations of Gravity. — The pendulum observations made in India have shown that there is a deficiency of attracting matter under that great continent, and this conclusion is borne out by a comparison of the geodetic and astronomical longitudes of stations on the east and west coast, from which it appears that the ocean bed exercises a stronger attraction than the raised land. In the Astronomische Nachrichten Herr Hann calls attention to this, and also to the circumstance that oceanic islands show an excess of attraction which cannot be accounted for by the nature of the rock of which they are composed. The theory that there are great cavities under the large continents appears hardly tenable, and the more probable supposition would seem to be that they rise above the sealevel by virtue of their specific lightness, floating perhaps like icebergs surrounded by a floe, with the molten liquid under a thin crust. There are, however, difficulties connected with precession and nutation and tides in a fluid interior, all of which Sir W. Thomson has pointed out, and we can only wait for further data. The balance of evidence, however, seems now to have changed, inclining to the hypothesis of a moderately thin crust with fluid or semi-fluid interior. Academy.