“I do not affirm that we are menaced with an earthquake,” answered Cyrus Harding, “may God preserve us from that!  No; these vibrations are due to the effervescence of the central fire.  The crust of the earth is simply the shell of a boiler, and you know that such a shell, under the pressure of steam, vibrates like a sonorous plate. it is this effect which is being produced at this moment.”

“What magnificent flames!” exclaimed Herbert.

At this instant a kind of bouquet of flames shot forth from the crater, the brilliancy of which was visible even through the vapors.  Thousands of luminous sheets and barbed tongues of fire were cast in various directions.  Some, extending beyond the dome of smoke, dissipated it, leaving behind an incandescent powder.  This was accompanied by successive explosions, resembling the discharge of a battery of machine-guns.

Cyrus Harding, the reporter, and Herbert, after spending an hour on the plateau of Prospect Heights, again descended to the beach, and returned to Granite House.  The engineer was thoughtful and preoccupied, so much so, indeed, that Gideon Spilett inquired if he apprehended any immediate danger, of which the eruption might directly or indirectly be the cause.

“Yes, and no,” answered Cyrus Harding.

“Nevertheless,” continued the reporter, “would not the greatest misfortune which could happen to us be an earthquake which would overturn the island?  Now, I do not suppose that this is to be feared, since the vapors and lava have found a free outlet.”

“True,” replied Cyrus Harding, “and I do not fear an earthquake in the sense in which the term is commonly applied to convulsions of the soil provoked by the expansion of subterranean gases.  But other causes may produce great disasters.”

“How so, my dear Cyrus?’

“I am not certain.  I must consider.  I must visit the mountain.  In a few days I shall learn more on this point.”

Gideon Spilett said no more, and soon, in spite of the explosions of the volcano, whose intensity increased, and which were repeated by the echoes of the island, the inhabitants of Granite House were sleeping soundly.

Three days passed by—­the 4th, 5th, and 6th of January.  The construction of the vessel was diligently continued, and without offering further explanations the engineer pushed forward the work with all his energy.  Mount Franklin was now hooded by a somber cloud of sinister aspect, and, amid the flames, vomiting forth incandescent rocks, some of which fell back into the crater itself.  This caused Pencroft, who would only look at the matter in the light of a joke, to exclaim,—­

“Ah! the giant is playing at cup and ball; he is a conjurer.”

In fact, the substances thrown up fell back again in to the abyss, and it did not seem that the lava, though swollen by the internal pressure, had yet risen to the orifice of the crater.  At any rate, the opening on the northeast, which was partly visible, poured out no torrent upon the northern slope of the mountain.