the precipice. "Say!" He sat up with a
start. "What's that?"

A metallic ray of light flashed out from the summit of Half Dome, then a
second and a third. The heads of both boys were craned backward on the
instant, agog with excitement.

"What a duffer!" Gus cried. "Why didn't he come down when it was cool?"

Hazard shook his head slowly, as if the question were too deep for
immediate answer and they had better defer judgment.

The flashes continued, and as the boys soon noted, at irregular
intervals of duration and disappearance. Now they were long, now short;
and again they came and went with great rapidity, or ceased altogether
for several moments at a time.

"I have it!" Hazard's face lighted up with the coming of understanding.
"I have it! That fellow up there is trying to talk to us. He's flashing
the sunlight down to us on a pocket-mirror--dot, dash; dot, dash; don't
you see?"

The light also began to break in Gus's face. "Ah, I know! It's what they
do in war-time--signaling. They call it heliographing, don't they? Same
thing as telegraphing, only it's done without wires. And they use the
same dots and dashes, too."

"Yes, the Morse alphabet. Wish I knew it."

"Same here. He surely must have something to say to us, or he wouldn't
be kicking up all that rumpus."

Still the flashes came and went persistently, till Gus exclaimed: "That
chap's in trouble, that's what's the matter with him! Most likely he's
hurt himself or something or other."

"Go on!" Hazard scouted.

Gus got out the shotgun and fired both barrels three times in rapid
succession. A perfect flutter of flashes came back before the echoes had
ceased their antics. So unmistakable was the message that even doubting
Hazard was convinced that the man who had forestalled them stood in some
grave danger.

"Quick, Gus," he cried, "and pack! I'll see to the horses. Our trip
hasn't come to nothing, after all. We've got to go right up Half Dome
and rescue him. Where's the map? How do we get to the Saddle?"

"'Taking the horse-trail below the Vernal Falls,'" Gus read from the
guide-book, "'one mile of brisk traveling brings the tourist to the
world-famed Nevada Fall. Close by, rising up in all its pomp and glory,
the Cap of Liberty stands guard----"

"Skip all that!" Hazard impatiently interrupted. "The trail's what we
want."

"Oh, here it is! 'Following the trail up the side of the fall will bring
you to the forks. The left one leads to Littl