The least exertion exhausted them.

One of the lanterns flickered out and the other was very dim.
At last Paul seized a hammer and going up the little iron ladder, struck three or four blows on the cover of the man-hole, under the impression that those above might hear.

The effort was too much for him and he fell to the floor where he laid in an almost unconscious condition.

He dimly remembered hearing the straining of chains, then the man-hole was opened and a voice inquired: "How is it ?" There was no answer to the inquiry and the rescuers only found out how it was when they entered the boat and dragged the three unconscious men out to light and air where they quickly recovered.

The inventor of the boat made an examination of her machinery and found that the valves had been tampered with and rendered useless.