“You don’t mean to say, captain,” interrupted Pencroft, “that we burn diamonds in our stoves in the shape of coal?”

“No, my friend,” replied Harding.

“However,” resumed Gideon Spilett, “you do not deny that some day the coal will be entirely consumed?”

“Oh! the veins of coal are still considerable, and the hundred thousand miners who annually extract from them a hundred millions of hundredweights have not nearly exhausted them.”

“With the increasing consumption of coal,” replied Gideon Spilett, “it can be foreseen that the hundred thousand workmen will soon become two hundred thousand, and that the rate of extraction will be doubled.”

“Doubtless; but after the European mines, which will be soon worked more thoroughly with new machines, the American and Australian mines will for a long time yet provide for the consumption in trade.”

“For how long a time?” asked the reporter.

“For at least two hundred and fifty or three hundred years.”

“That is reassuring for us, but a bad look-out for our great-grandchildren!” observed Pencroft.

“They will discover something else,” said Herbert.

“It is to be hoped so,” answered Spilett, “for without coal there would be no machinery, and without machinery there would be no railways, no steamers, no manufactories, nothing of that which is indispensable to modern civilization!”

“But what will they find?” asked Pencroft.  “Can you guess, captain?”

“Nearly, my friend.”

“And what will they burn instead of coal?”

“Water,” replied Harding.

“Water!” cried Pencroft, “water as fuel for steamers and engines! water to heat water!”

“Yes, but water decomposed into its primitive elements,” replied Cyrus Harding, “and decomposed doubtless, by electricity, which will then have become a powerful and manageable force, for all great discoveries, by some inexplicable laws, appear to agree and become complete at the same time.  Yes, my friends, I believe that water will one day be employed as fuel, that hydrogen and oxygen which constitute it, used singly or together, will furnish an inexhaustible source of heat and light, of an intensity of which coal is not capable.  Some day the coalrooms of steamers and the tenders of locomotives will, instead of coal, be stored with these two condensed gases, which will burn in the furnaces with enormous calorific power.  There is, therefore, nothing to fear.  As long as the earth is inhabited it will supply the wants of its inhabitants, and there will be no want of either light or heat as long as the productions of the vegetable, mineral or animal kingdoms do not fail us.  I believe, then, that when the deposits of coal are exhausted we shall heat and warm ourselves with water.  Water will be the coal of the future.”

“I should like to see that,” observed the sailor.

“You were born too soon, Pencroft,” returned Neb, who only took part in the discussion by these words.