their deadly fumes and
pouring forth their sluggish, boiling lava. The scene about us now was
lighted in a horrible blue-green glare. A great cloud of thin smoke
gathered, hung poised a moment, and then rolled slowly away--its deadly
fumes hanging low to the ground and spreading ever wider as though eager
to clutch the unsuspecting city in their deadly embrace.

The entire face of the cliff was now covered with the crawling blue fire,
lapping avidly about with its ten-foot tongues. We drew back, staring
silently at each other's ghastly green faces.

"Let's--let's get away," Mercer whispered finally. "No use staying here
now."

We hurried back to the nearest place where one of our projectors was set
up. The two men guarding it looked at us anxiously, and smiled
triumphantly when Miela told them what we had done. We stood beside them a
moment, then Miela and I climbed to an eminence near by from which we had
an unobstructed view of the city.

The light-barrage still held steady. The individual, higher-powered
projectors as before swung their beams lazily about the country. We sat
partly in the shelter of a huge bowlder, behind which we could have
dropped quickly had one of them turned our way.

"Soon it will be there," Miela said softly, when we had been sitting quiet
for a time.

I did not answer. It was indeed too solemn a thing for words, this
watching from the darkness while an invisible death, let loose by our own
hands, stole down upon our complacent enemies.

A few moments more we watched--and still the scene before us showed no
change. Then, abruptly, the lights seemed to waver; some of the beams
swung hurriedly to and fro, then remained motionless in unusual positions,
as though the men at their levers in sudden panic had abandoned them.

My heart was beating violently. What hidden tragedy was being enacted
behind that silent barrier of light? I shuddered as my imagination
conjured up hideous pictures of that unseen death that now must be
stalking about those city streets, entering those homes, polluting the air
with its stifling, noisome breath, and that even at this distance seemed
clutching at my own lungs.

I suppose the whole thing _did_ last only a moment. There was little in
what we saw of significance had we not known. But we did know--and the
knowledge left us trembling and unnerved.

I leaped to my feet, pulling Miela after me, and in a few moments more we
were back beside the projector we h