about six o’clock
But still the professor kept the _ Mermaid _ sinking . Every now and again he would take an observation , but only found the impenetrable darkness surrounded them . `` We must arrive somewhere , soon , '' he muttered . It was about six o'clock that night that the alarm bell set up a sudden ringing . The professor who was making some calculations on a piece of paper jumped to his feet , and so did a number of the others . `` We are nearing the bottom ! '' he cried .