“You can be sure he’s down,” Gus spoke up at last.  “It’s mighty warm on that naked rock with the sun beating down on it at this time of year.  That was our plan, you know, to go up early and come down early.  And any man, sensible enough to get to the top, is bound to have sense enough to do it before the rock gets hot and his hands sweaty.”

“And you can be sure he didn’t take his shoes with, him.”  Hazard rolled over on his back and lazily regarded the speck of flag fluttering briskly on the sheer edge of 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.”