The professor's small audience duly expressed their thanks for the extremely interesting lecture to which they had just been treated, and then the party retreated to the pilot-house; the door was closed to exclude the cold air of the upper regions which they were about to visit; and an ascent was made to an altitude of eight thousand feet, where the night was passed in an atmosphere so completely motionless that, on their descent next morning, Lieutenant Mildmay's observations showed them to be in the exact spot which they had occupied on the previous evening. It was decided over the breakfast-table that morning, that the journey northward should be prosecuted, as far as possible, upon the surface of the sea; and the _Flying Fish_ was accordingly put in motion on the required course immediately upon her descent. Their rate of progress was particularly slow, not exceeding, on the average, a speed of six miles per hour, as drift ice was remarkably abundant, mostly in small detached blocks, though they occasionally encountered a floe of several acres in extent; and, far away to the northward, quite a large assemblage of bergs were seen. This slow rate of progress would have been wearisome to a veteran Arctic navigator in possession of such means for the accomplishment of a quick passage as those enjoyed by the inmates of the _Flying Fish's_ pilot-house; but to them everything was novel and interesting, and, almost before they knew it, they found themselves in the immediate vicinity of the bergs. These varied greatly in size, some of them being no larger than a dwelling-house of moderate dimensions, whilst others fully equalled, if, indeed, they did not exceed, the proportions of the monsters seen on the previous evening. They were grouped so closely together that a passage between them seemed to be not wholly unattended with danger; and the party were in the act of discussing the question which channel it would be most prudent to take, their eyes being meanwhile fixed on the huge towering cliffs of ice before them, when a gigantic overhanging mass was seen to detach itself from its parent berg and plunge, a distance of some two hundred and fifty feet, with a terrific splash into the water and disappear. The deep thunderous roar of its plunge smote the ears of the watchers next moment, and they looked on with breathless interest to see what would follow. The mass, from its enormous size, would weigh, they considered, fully five thousand tons; and they were not surprised to see that the loss of so much weight had seriously disturbed the balance of the berg, which at once began to rock ponderously to and fro, creating a terrific commotion in the water when conjoined with that caused by the plunge into the sea and the reappearance a second or two later of the detached mass. The sea was seen to heap itself up in a long well- defined ridge, similar--though, of course, on a tremendously magnified