d opened their mouths. It appeared that for
yet a little while they were to remain in ignorance of the precise
meaning of the experiment.

The glass of the bell was clouding. A swirling, milky vapor, not unlike
fog, was filling the bell from top to bottom.

The dog, rapidly being hidden from sight by the gathering mist, suddenly
stopped its antics and stood still in the center of the bell as though
overcome by surprise and indecision. Motionless, staring vacantly, it
stood there for an instant--then was concealed completely by the rolling
vapor.

But just before it disappeared, Jim turned to Denny in astonishment, to
see if Denny had observed what he had; namely, that the fog seemed not
to be gathering from the air penned up in the bell, but in some strange
and rather awful way to be exuding _from the body of the dog itself_!

* * * * *

The two stared back at the bell again, neither one sure he had been
right in his impression. But now the glass was entirely opaque. So thick
was the vapor within that it seemed on the point of turning to a liquid.
Inside, swathed in the secrecy of the fleecy folds of mist--what was
happening to the dog? The two men could only guess.

Matt glanced up at an electric clock with an oversized second hand. His
fingers moved nervously on the switch, then threw it to cut contact. The
dynamo keened its dying note. A silence so tense that it hurt filled the
great laboratory.

All eyes were glued on the bell.

The thick vapor that had been swirling and crowding as if to force
itself through the glass, grew less restive in motion. Then it began to
rise, ever more slowly, toward the top.

More and more compactly it packed itself into the arched glass dome, the
top layers finally resembling nothing so much as cloudy beef gelatin.
And now these top layers were solidifying, clinging to the glass.

Meanwhile, the bottom line of the vapor was slowly rising, an inch at a
time, like a shimmering curtain being raised from a stage floor. At last
ten inches showed between the pedestal and the swaying bottom of the
almost liquid vapor. Jim and Denny stooped to peer under the blanket of
cloud. The dog! In what way had it been affected?

Again they exclaimed aloud, involuntarily, unconsciously.

There was no dog to be seen.

* * * * *

With about fourteen clear inches now exposed, they looked a second time,
more intently. But their fi