The infernal machine--for such it was--was an ingeniously-constructed piece of work. The hollow shell of papier-mâché was made to resemble a lump of coal. Within was a slab of wet gun-cotton, while to make up the deficiency of weight the hollow was filled with water. Fortunately the bomb must have been cracked in contact with lumps of genuine coal, for the water had escaped. The contrivance would have been thrown into the furnace, with disastrous results; but Malcolm's astuteness had saved the situation.