1874.] Presents. 329 



creased, its volume remaining constant, or the thickness being constant, 

 a portion of the volume must be extruded. The former supposition is 

 not admissible, as the epoch of mountain-building has apparently ceased ; 

 adopting the second, the author calculates the volume of matter that 

 must be crushed and extruded from, the shell in order that it may remain 

 in contact with the nucleus. He tabulates these results for the four 

 assumed thicknesses of shell, and shows that the amount of crushed 

 and extruded rock necessary for the heat for the support of existing 

 volcanic action is supplied by that extruded from the shell of between 

 600 and 800 miles thickness, and that the volume of material, heated or 

 molten, annually blown out from all existing volcanic cones, as estimated 

 in his former paper, could be supplied by the extruded matter from a 

 shell of between 200 and 400 miles in thickness. 



On data which seem tolerably reliable the author has further been 

 enabled to calculate, as he believes for the first time, the actual amount 

 of annual contraction of our globe, and to show that if that be assumed 

 constant for the last 5000 years, it would amount to a little more than a 

 reduction of about 3' 5 inches on the earth's mean radius. This quantity, 

 mighty as are the effects it produces as the efficient cause of volcanic 

 action, is thus shown to be so small as to elude all direct astronomical 

 observation, and, when viewed in reference to the increase of density due 

 to refrigeration of the material of the shell, to be incapable of producing, 

 during the last 2000 years, any sensible effect upon the length of the 

 day. The author draws various other conclusions, showing the support 

 given by the principal results of this entirely independent investigation 

 to the verisimilitude of the views contained in his previous memoir. 



Presents received, April 16, 1874. 



Transactions. 



Batavia : Koninklijke Katuurkundige Vereeiiigiug in Kederlandsch 



Indie. Natuurkundig Tijdschrift voor ]S T ederlandsch Indie. 



Deel XXXII. An. 4-6. Svo. 1873. The Society. 



Danzig: Xaturforschende Gesellschaft. Schriften. Neue Folge. 



Baud III. Heft 2. Svo. 1873. (Another copy, with photographs.) 



The Society. 

 Goteborg : Kongl. Vetenskaps och Vitterhets Samhalle. Handlmgar. 



Ny Tidsfoljd. 12 Haftet. Svo. 1873. The Society. 



Harlem: Societe Hollandaise des Sciences. Archives Neerlandaises 



des Sciences Exactes et Naturelles. Tome VIII. Liv. 3, 4. 8vo. 



La Haye 1873. The Society. 



