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 than the other, and even with this advantage the crevasse seemed dangerously wide. One is liable to underestimate the width of crevasses where the magnitudes in general are great. I therefore stared at this one mighty keenly, estimating its width and the shape of the edge on the farther side, until I thought that I could jump it if necessary, but that in case I should be compelled to jump back from the lower side I might fail. Now, a cautious mountaineer seldom takes a step on unknown ground which seems at all dangerous that he cannot retrace in case he should be stopped by unseen obstacles ahead. This is the rule