Travers. — On the Causes of Volcanic Eruptions. 337 



gradual solidification of films on the surface of the diminishing 

 nucleus. 



The effect of the operations referred to upon the ultimate 

 form of a spherical mass of fused matter, occupying the position 

 and having the motions of the Earth, would, I think, be to pro- 

 duce, or, at all events, materially to assist in producing, the form 

 which the Earth now presents. Eadiation from such a mass 

 would, in the absence of any local compensating action, be equal 

 from every part of the surface ; but from the moment that a 

 fixed axis of rotation had been established under the paramount 

 influence of the Sun's attraction, that radiation would proceed 

 most rapidly at the poles, diminishing gradually towards the 

 equator. 



The result of the more rapid radiation in circumpolar 

 regions would be to reduce the sphere to a spheroid, by the pres- 

 sure of the contracting outer crust within those areas upon the 

 molten internal mass, which, in its turn, would necessarily press 

 outwards upon the more plastic materials in equatorial regions, 

 until equilibrium had been established. This view is supported 

 by the distribution of volcanoes on the surface of the Earth : for, 

 with the exception of Hecla, in Iceland, in latitude 65° North, and 

 Mount Ei'ebus, on the Antarctic Land, in about the same latitude 

 South, active volcanic action is most intense within tropical re- 

 gions, and extends but little into the limits of the temperate zone. 

 This fact appears to indicate that the loss of heat which the 

 earth originally sustained, and is still suffering, is largely com- 

 pensated within the tropics, and for some distance on each side 

 of them, by that which it receives from the sun's radiation, and, 

 consequently, that the molten material in the interior of the 

 earth is exposed, within that area, to pressure less effective to 

 prevent earthquakes and resulting volcanic phenomena, than 

 it is subject to within the circumpolar and immediately adjacent 

 regions. 



It is, no doubt, difficult to apply the mind to the considera- 

 tion of operations such as these in connection with a mass of 

 such enormous dimensions as our globe ; but it is very clear 

 that, with the exception of the cooling of its surface to such a 

 degree as to cause any great amount of contraction, operations 

 of this very nature must now be going on in the great planet 

 Jupiter, I cannot say to what extent the dynamical heat, 

 generated by the condensation of the cosmical matter of which 

 that planet is composed, and which is being lost by radiation 

 into space, is compensated from outer sources. Those who are 

 curious on this subject may consult the views propounded by 

 Mr. Mattieu Williams, in his work on " The Fuel of the Sun," 

 and the very similar views as to the maintenance of the sun's 

 heat propounded by the late Sir W. Siemens in the columns of 

 " Nature." It is clear, however, that in the case of our globe, 



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