"Well, I will tell you that true savants, amongst them Poisson, have demonstrated that if a heat of 360,000 degrees [1] existed in the interior of the globe, the fiery gases arising from the fused matter would acquire an elastic force which the crust of the earth would be unable to resist, and that it would explode like the plates of a bursting boiler." "That is Poisson's opinion, my uncle, nothing more." "Granted. But it is likewise the creed adopted by other distinguished geologists, that the interior of the globe is neither gas nor water, nor any of the heaviest minerals known, for in none of these cases would the earth weigh what it does." "Oh, with figures you may prove anything!" "But is it the same with facts! Is it not known that the number of volcanoes has diminished since the first days of creation? and if there is central heat may we not thence conclude that it is in process of diminution?" "My good uncle, if you will enter into the legion of speculation, I can discuss the matter no longer." "But I have to tell you that the highest names have come to the support of my views. Do you remember a visit paid to me by the celebrated chemist, Humphry Davy, in 1825?" "Not at all, for I was not born until nineteen years afterwards." "Well, Humphry Davy did call upon me on his way through Hamburg. We were long engaged in discussing, amongst other problems, the hypothesis of the liquid structure of the terrestrial nucleus. We were agreed that it could not be in a liquid state, for a reason which science has never been able to confute." [1] The degrees of temperature are given by Jules Verne according to the centigrade system, for which we will in each case substitute the Fahrenheit measurement. (Tr.) "What is that reason?" I said, rather astonished. "Because this liquid mass would be subject, like the ocean, to the lunar attraction, and therefore twice every day there would be internal tides, which, upheaving the terrestrial crust, would cause periodical earthquakes!" "Yet it is evident that the surface of the globe has been subject to the action of fire," I replied, "and it is quite reasonable to suppose that the external crust cooled down first, whilst the heat took refuge down to the centre." "Quite a mistake," my uncle answered. "The earth has been heated by combustion on its surface, that is all. Its surface was composed of a great number of metals, such as potassium and sodium, which have the peculiar property of igniting at the mere contact with air and water; these metals kindled when the atmospheric vapours fell in rain upon the soil; and by and by, when the waters penetrated into the fissures of the crust of the earth, they broke out into fresh combustion with explosions and eruptions. Such was the cause of the numerous volcanoes at the origin of the earth." "Upon my word, this is a very clever hypothesis," I exclaimed, in spite rather of myself.