Vulcan for the sake of wresting from the rocky soil its
vast deposits of rare ores, and a great number of mining operations are
continually in progress. All of these are commercial projects and are
worked by adventurous seekers of fortune, save only the penal colony
known as Vulcan's Workshop: But no Terrestrial or Martian, however
greedy for riches, would dare to remain longer than two lunar months,
which is the average time limit of human endurance. Only the condemned
remain, and these remain to die.

* * * * *

Though hardly more than two hundred miles in diameter, Vulcan is
possessed of a surface gravity almost six times greater than that on
Earth. This is due to the planet's core of neutronium, the densest known
substance of the universe, a little understood concentration of matter
whose atoms comprise only nuclei from which all negative electrons have
been stripped by some stupendous cataclysm of nature.

And so it was that Luke Fenton, uninsulated from the tremendous gravity
pull when he stepped from the charged metal of the runway, was
struggling against his own bodily weight, suddenly increased to more
than twelve hundred pounds.

Doggedly, the Earthman pitted his mighty sinews against the force he
could not understand. Here was an intangible thing, yet it was a power
that challenged his own brute strength, and he exerted himself to the
limit in accepting the challenge. With legs spread wide and with sweat
oozing from every pore, he heaved himself erect, straightening knees and
spine and standing there firmly on his two feet.

"He's carrying it!" came the husky whisper of a guard. "This bird _is_
tough."

Craftily, Luke bared his white, even teeth in a good-humored grin. He
had seen what they were doing with the other prisoners, fitting them one
by one with the strange bulky breeches--garments that gave forth a faint
greenish glow like that of the runway. And each of the men, so attired,
was enabled somehow to get to his feet easily and walk about as if
unhampered by the force which had flattened him to the rocks and which
still held Luke's straining body in its grip.

* * * * *

The yellow-skinned guard, a Terrestrial of Asiatic origin, was solemnly
engaged now in lacing the slitted legs of a similar garment to Luke's
rigid nether limbs. Yet there was no cessation of that awful weight when
the thing was done. The guard