ike the roar of a
volcano and an answering echo from the black dome overhead. This died
away and was succeeded by a crash of musical thunder that thrilled
Johnston's being to its very core. Branasko's face was aglow with
enthusiasm.

"Grand, glorious!" he ejaculated, "but if only you could see the
lightning and the dawn in the east you would remember it all your life.
The sunlight is cut off from Alpha by the clouds, and there is no light
except the wonderful effects in the sky."

Johnston had gone back to the wheel and was examining it curiously.

"I have a mind to turn off the current for a moment anyway," he said
doggedly; "if the sun is hidden they would not discover it."

Branasko came to him, a weird look of interest in his eyes. "That
is true," he said; "besides, what matters it? We may not live to see
another day."

Johnston acted on a sudden impulse. He intended only to frighten
Branasko by moving the wheel slightly, and he had turned it barely an
eighth of an inch, when, as if controlled by some powerful spring, it
whirled round at a great rate, making a loud rattling noise. To their
dismay the light went out.

"My God! what have I done?" gasped the American in alarm.

"Settled our fate, I have no doubt," muttered the Alphian from the
darkness.

Johnston had recoiled from the whirling wheel, and now cautiously groped
back to it, and attempted to turn it. It would not move.

"It has caught some way," he groaned under his breath.

"And we have no light to find the cause of the trouble," added the
Alphian, who had knelt down and was feeling about the wheel. Presently
he rose.

"I give it up," he sighed, "I cannot understand it. The machinery is
somewhere inside."

"It has grown colder," shuddered Johnston.

"We were warmed by the light, of course," remarked Branasko, "and now we
feel the dampness more. We are going at a frightful speed."

Just then there was a jar, and the sun swung so violently from side to
side that the two men were prostrated on the floor. The speed seemed to
slacken.

"I wonder if we are going to stop," groaned the American, and he sat
up and held to Branasko. "Perhaps they will draw us back to rectify the
mistake, and then----"

"It cannot be done," interrupted the Alphian. "The machinery runs only
one way. We shall simply have to finish our journey in darkness."

"They may catch us on the other side before the sun starts back through
the tunnel," suggested the America