0. Fisher — Rival Theories of Cosmogony. 421 



But an observation of interest as bearing upon the present 

 question was made by Professor Bartoli. He found that the 

 temperature of the lava issuing from a subterranean outlet at 

 Etna was 1060° C. or 1932° Fahr. 



Now if we calculate the increase of density corresponding 

 to the above temperature it comes out 0*120. The rate of 

 increase of density near the surface is about 0*056 for 20 

 miles. Hence the depth, at which this lava temperature would 

 according to the hypothesis be produced, would be about 43 

 miles. If we calculate the depth at which the same tempera- 

 ture might now be expected to occur with the commonly 

 accepted gradient of 1° Fahr. for 60 feet, it appears to be 22 

 miles. It seems then that the hypothesis, that the internal 

 densities are due to the condensation of matter of surface den- 

 sity, will not account for a temperature gradient originally as 

 high as at present. Nevertheless the above observation upon 

 the temperature of lava, and the comparatively small depth, 

 20 miles, at which condensation of rock would be capable of 

 producing it, together with the small amount of condensation 

 necessary, viz., 0*041, render it quite probable that fusion may 

 have ensued in the deep interior without the necessity of a 

 greater amount of condensation than such materials might be 

 supposed capable of under the enormous pressure to which 

 they would be subjected, even allowing for the increase of the 

 melting point under pressure. In this case we might accept 

 the second alternative, and attribute the high density of the 

 more central parts to the accumulation of the heavier elements 

 by gravitation. In this manner the materials of iron meteor- 

 ites would fall toward the center. It will be noticed that a 

 compression less than would be requisite of itself to produce 

 the necessary density would be sufficient to produce the requis- 

 ite temperature for fusion. But while any stratum was cooling 

 by the conduction upwards of its own heat of compression, it 

 would be receiving heat from regions below, where, so long as 

 condensation was going on, the materials would grow hotter 

 and hotter. It seems therefore possible that the upper layers, 

 forming what we call the crust of the earth, may have received 

 sufficient heat supplied from below to render the temperature 

 gradient at the present time higher than it was originally, and 

 that even those Archean rocks, which are by many thought to 

 have been once melted, do not necessarily prove that the earth 

 was not built of cold meteorites. 



The presence of water upon the earth has to be accounted 

 for, and the meteoric theory does not easily lend itself for this 

 purpose. Not only is water present in the ocean and in the 

 atmosphere, but also in a state of solution in the interior, as is 

 testified by the enormous amount of steam emitted by vol- 



