For several days the colonists were actively employed in haymaking and the harvest.  Before putting their project of exploring the yet unknown parts of the island into execution, they wished to get all possible work finished.  It was also the time for collecting the various vegetables from the Tabor Island plants.  All was stowed away, and happily there was no want of room in Granite House, in which they might have housed all the treasures of the island.  The products of the colony were there, methodically arranged, and in a safe place, as may be believed, sheltered as much from animals as from man.

There was no fear of damp in the middle of that thick mass of granite.  Many natural excavations situated in the upper passage were enlarged either by pick-axe or mine, and Granite House thus became a general warehouse, containing all the provisions, arms, tools, and spare utensils—­in a word, all the stores of the colony.

As to the guns obtained from the brig, they were pretty pieces of ordnance, which, at Pencroft’s entreaty, were hoisted by means of tackle and pulleys, right up into Granite House; embrasures were made between the windows, and the shining muzzles of the guns could soon be seen through the granite cliff.  From this height they commanded all Union Bay.  It was like a little Gibraltar, and any vessel anchored off the islet would inevitably be exposed to the fire of this aerial battery.

“Captain,” said Pencroft one day, it was the 8th of November, “now that our fortifications are finished, it would be a good thing if we tried the range of our guns.”

“Do you think that is useful?” asked the engineer.

“It is more than useful, it is necessary!  Without that how are we to know to what distance we can send one of those pretty shot with which we are provided?”

“Try them, Pencroft,” replied the engineer.  “However, I think that in making the experiment, we ought to employ, not the ordinary powder, the supply of which, I think, should remain untouched, but the pyroxyle which will never fail us.”

“Can the cannon support the shock of the pyroxyle?” asked the reporter, who was not less anxious than Pencroft to try the artillery of Granite House.

“I believe so.  However,” added the engineer, “we will be prudent.”  The engineer was right in thinking that the guns were of excellent make.  Made of forged steel, and breech-loaders, they ought consequently to be able to bear a considerable charge, and also have an enormous range.  In fact, as regards practical effect, the transit described by the ball ought to be as extended as possible, and this tension could only be obtained under the condition that the projectile should be impelled with a very great initial velocity.

“Now,” said Harding to his companions, “the initial velocity is in proportion to the quantity of powder used.  In the fabrication of these pieces, everything depends on employing a metal with the highest possible power of resistance, and steel is incontestably that metal of all others which resists the best.  I have, therefore, reason to believe that our guns will bear without risk the expansion of the pyroxyle gas, and will give excellent results.”