It was liable to give out at any time, and then a horrible death by asphyxiation must be the result.
Truly this was a dreadful thing to contemplate.
But Frank compressed his lips tightly and went resolutely into the pilot-house.
As nearly as he was able to plan it, he started the Dart in what he believed was a direct course out of the valley.
The boat shot onward through the water like an arrow.
Miles were covered, but yet there was no indication that they were approaching a coast.
A week passed thus.
It was a period of anxiety, of mental worriment and of almost despair.
Heretofore no thought had been given to the chemical generators, for had they failed it was always known that a supply of fresh air could be obtained by almost instantly rising to the surface.
But now that it seemed certain that the boat could not rise, all depended upon the efficacy of the generators.