rently into a brown study. His eyes
were fixed impatiently on the widespread ocean.

Our voyage now became monotonous and uniform. Dull as it has become, I
have no desire to have it broken by any repetition of the perils and
adventures of yesterday.

Thursday, August 20th. The wind is now N. N. E., and blows very
irregularly. It has changed to fitful gusts. The temperature is
exceedingly high. We are now progressing at the average rate of about
ten miles and a half per hour.

About twelve o'clock a distant sound as of thunder fell upon our ears. I
make a note of the fact without even venturing a suggestion as to its
cause. It was one continued roar as of a sea falling over mighty rocks.

"Far off in the distance," said the Professor dogmatically, "there is
some rock or some island against which the seal lashed to fury by the
wind, is breaking violently."

Hans, without saying a word, clambered to the top of the mast, but could
make out nothing. The ocean was level in every direction as far as the
eye could reach.

Three hours passed away without any sign to indicate what might be
before us. The sound began to assume that of a mighty cataract.

I expressed my opinion on this point strongly to my uncle. He merely
shook his head. I, however, am strongly impressed by a conviction that I
am not wrong. Are we advancing towards some mighty waterfall which shall
cast us into the abyss? Probably this mode of descending into the abyss
may be agreeable to the Professor, because it would be something like
the vertical descent he is so eager to make. I entertain a very
different opinion.

Whatever be the truth, it is certain that not many leagues distant there
must be some very extraordinary phenomenon, for as we advance the roar
becomes something mighty and stupendous. Is it in the water, or in the
air?

I cast hasty glances aloft at the suspended vapors, and I seek to
penetrate their mighty depths. But the vault above is tranquil. The
clouds, which are now elevated to the very summit, appear utterly still
and motionless, and completely lost in the irradiation of electric
light. It is necessary, therefore, to seek for the cause of this
phenomenon elsewhere.

I examine the horizon, now perfectly calm, pure, and free from all haze.
Its aspect still remains unchanged. But if this awful noise proceeds
from a cataract--if, so to speak in plain English, this vast interior
ocean is precipitated into a lower basin--if these