He went very carefully, however.

His foot tried each round, as some of them were worm-eaten.

A false step would entail a deadly fall, through this space of fifteen hundred feet.

He counted each landing as he passed it, knowing that he could not reach the bottom of the shaft until he had left the thirtieth.

Once there, he would have no trouble, so he thought, in finding the cottage, built, as we have said, at the extremity of the principal passage.
Jack Ryan went on thus until he got to the twenty-sixth landing, and consequently had two hundred feet between him and the bottom.
Here he put down his leg to feel for the first rung of the twenty-seventh ladder.