About twelve o'clock
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 sea lashed to fury by the wind , is breaking violently . ''