The spacing of the ties was not regular, and if he stepped short, or too far, he would go through.

Then, if he did not strike a brace, he would fall upon the rocks in the stream.

All the same, he saw the blaze of the head-lamp pick out the trees across the ravine and sprang on to the bridge.
Somehow he hit the ties; perhaps by subconscious judgment, and perhaps by good luck.

Then he felt loose gravel under his feet and thrilled with a strange fierce satisfaction.

His breath was labored and his body wet by sweat, but the moving beam had not reached the lamp.