Baron Humboldt on the Luminousness of the Earth. 339 



tusks of the Dicynodon, though similar, in their origin from 

 maxillary bones and downward direction, to the tusks of the 

 Walrus, are so much shorter, at least in the single specimen 

 in which their entire length is shewn, that they could not be 

 available in locomotion. I conclude, therefore, from their shape, 

 proportional length, sharp points, and dense texture, that the 

 tusks of the Dicynodon were applied by the living animal 

 either for the pm-pose of killing its prey, or of defending itself 

 from its foes, or in both acts; and that they are offensive and 

 defensive arms. 



A further insight into the habits and mode of life of the 

 Dicynodons may reasonably be expected to follow the exami- 

 nation of the skeleton of the trunk and the organs of locomo- 

 tion. This will form the subject of a subsequent memoir ; 

 but the vertebrae of the Dicynodon present the sub-biconcave 

 structure common to most of the older extinct saurians, which 

 structure, in comparison with the ball and socket vertebrae of 

 the modern species, indicates a more aquatic and perhaps 

 marine theatre of life for the amphibia which swarmed in 

 such plenitude of development and diversity of forms during 

 the ancient secondary periods of the geological history of this 

 planet. — Proceedings of the Geological Society — vide Transac- 

 tions of the Geological Society for Messrs Bain and Onsen's 

 Memoirs in full. 



On the Luminousness of the Earth. By Baron Von 

 Humboldt. 



If the luminous phenomenon which we ascribe to a galvanic 

 current, i. e., a movement of electricity in a circuit returning into 

 itself, be designated by the indefinite name of the Northern 

 light, or the Polar light, nothing more is thereby implied than 

 the local direction in which the beginning of a certain luminous 

 phenomenon is most generally, but by no means invariably, 

 seen. What gives this phenomenon its greatest importance, is 

 the fact which it reveals, viz., that the earth is luminous ; that 

 our planet, besides the light which it receives from the central 

 body, the sun, shews itself capable of a proper luminous act or 



