"stop her!" it was ned's voice in quick command. the young aeronaut, peering over the side of the car of the cibola into the black night, had suddenly seen something that prompted the order. it was a distant flash of light. this was followed by an echoing explosion. the other boys heard the explosion and all instantly knew that it was a shot from a firearm. almost before alan could shut off the power ned had disappeared into the cabin to help head the balloon in the direction of the spurt of fire. the cibola slackened speed and they waited, drifting slowly toward the east. then, suddenly, and almost together came two streaks of fire and two more explosions.
"one of them might mean a signal," said ned gravely, "but they were not from the same spot. if it were elmer he would have the three fires. if it is elmer and buck and they can't make a fire and are shooting i am afraid it means trouble."
"it may mean indians," suggested bob, "and they may have put out their fires for safety."
"they might even be holding off an attack of some kind," added alan anxiously.
just then there was another crack of a firearm now a little nearer. the cibola was drifting directly toward the sound, but very slowly, and would soon have lost all headway.
"i don't want to be presumptuous," said bob in a low voice, "but can't we land and find out what the trouble is?"
"we can find out without landing," replied alan.
it was so dark in the cabin that the boys could only dimly see each other, but ned was groping about near the silent engine. in a moment he had secured from the ammunition case a storage electric light, and cautiously shading the lens with his cap he asked bob to hold it. then he turned to his chum.
"i didn't know just how we would use our little drop light," he began; "but it seems that the idea wasn't half bad. there is a tribe of indians not far from here that would steal a horse or cut a man's throat quickly enough—the renegade or southern utes." as he spoke he was digging in a chest extracting various small parcels. "not even the other indians have any use for the utes. and there is only one thing to do. we must first find out if our friends are below."
with the help of the flashlight bob could we that ned held in his hand a large, high candle-power incandescent bulb and was adjusting it in a silver reflector.
"with an electric light?" exclaimed bob.
"why not?" replied ned. "and the help of our little dynamo."
ned took the flashlight, held it under his coat, and crawled around in front of the silent engine. "it's here," he explained for bob's benefit, "and i am just throwing the gear onto the propeller shaft."
"well, if you are afraid to show this little light why aren't you afraid to show a brighter light?" asked the observing reporter.
alan answered him.
"we are only afraid because it might draw an attack from some observer. balloonists are never safe from meddlesome persons or worse. but there isn't the same danger if the light isn't on the balloon."
"sure," said bob. "i understand that. but you can't hold it very far away."
"no," answered ned, "that's why we braided two good copper wires in our drag rope." as he said this he opened the trap door in the floor of the cabin and feeling about in the dark soon had hold of the coiled drag.
"i guess i'm dull," began bob.
"no," interrupted alan, "only you haven't given two or three years to figuring out the possibilities of an air ship."
ned was attaching the bulb, reflector down, to the end of the rope.
"that rope is three hundred feet long. a light at the end of it is quite a way from our bag.
"oh, i see," exclaimed bob at last. "if we find indians and they shoot at our searchlight they are pretty sure to miss us."
"that is the theory," answered ned.
and then the plan in ned's mind was explained. the engine was to be started at quarter speed, which meant that the sound would be imperceptible; and, lying on the floor of the cabin, ned was to direct the movements of the ship, with alan at the rudder wheel and bob at the aeroplane guider.
"a quarter to ten o'clock," said ned glancing at his watch as he shut off the concealed flashlight, "and now start her up."
as alan started the engine and it began to turn the propeller they could tell by the light breeze that the car was moving again, but very slowly. the other boys could also hear ned delicately paying out the long drag rope. at last it was all out. then ned crawled forward again to the dynamo and up to the partly open floor of the car and whispered that he was ready. the multiple gear was already speeding the little generator swiftly.
"lie down on the floor and watch," murmured ned softly, "i'm going to turn her on."
alan and bob did so. as their two heads filled the open trap in the cabin floor there was a click and then, as if some necromancy had focused the sun on a part of the darkened world, a circle of light seemed to spring out of the desert beneath. yellow, with here and there a ragged rock and a sage brush or two, the shadows of the rocks and brush black like spilled ink, and the sand glaring back at them with almost quivering brightness, the circle shot back and forth as the light followed the swinging rope. but no living thing was in sight. a click and all was black again.
"nothing doing," exclaimed bob.
"wait," suggested ned, "persons we couldn't see may have seen them."
almost as he spoke there was another quick report.
"did you see the flash, alan?" asked ned eagerly, for he had been busy with the dynamo.
but alan was already at the wheel, and again the car swung from its course.
"wait," he exclaimed, "turn it on again when i give the word."
after perhaps two minutes he gave the signal and again ned flashed the gleaming bulb. again the circle sprang apparently out of the black ground. as the car drifted forward the black blotched golden sand ran the opposite way like a whirling panorama. a coyote sprang, dazed, from a clump of bushes and back again, but that was all.
"give him another chance," whispered alan, and the light flashed out.
"listen," exclaimed bob breathlessly, "wasn't that a cry?"
another moment and the sound came again.
"elmer!" exclaimed the two air ship boys together.
the cibola swung instantly at alan's quick touch. again the light flashed. sand and rock and brush. the brilliant circle of light shot here and there, but the anxious watchers saw sign of neither friend nor foe. then like a flash the level plain dropped into the sudden slope of a coulee and the darker shadow of water blotted out the glare of sand.
"the river," whispered ned. "now watch sharp."
as the light was blotted out this time alan swung the wheel again. he knew instantly that they were on the wrong track, as they were going east and crossing the chusco. elmer and buck would not cross the river. the camp was to be on the west side.
"follow the river," ordered ned quickly; "the west shore."
in order that the cibola might be laid on the new course ned threw on the light switch again. as he did so and the light flashed there was the sharp crack of a rifle and the light was gone.
"turn her on," exclaimed alan; "i want to get a line on the river bed."
ned laughed. "i'll need a new bulb first. some one down below turned it off."
"what?" exclaimed the other boys together.
"shot out," calmly retorted ned.
