ked. "Are you able to
tell?"

Professor Maddox nodded. "The photographs show us what has happened, but
they reveal nothing about how or why. We can see the surface tension of
the two pieces of metal has obviously broken down so that the small
energy of motion possessed by the molecules has permitted them to move
toward each other, with a consequent mixing of the two metals. It has
turned them quite literally into a single piece, the most effective kind
of weld you can imagine."

"What would cause the surface tension to break down like that?" Ken
asked.

"That is what remains for us to find out. We don't have the faintest
idea what has caused it. It becomes especially baffling when we recall
that it has happened, not in a single isolated instance, but all over
the world."

"You would think the metals would have become soft, like putty, or
something, for a thing like that to happen to them," said Joe.

"It would be expected that the hardness would be affected. This is not
true, however. The metals seem just as hard as before. The effect of
mixing seems to take place only when the metals are in sliding motion
against one another, as in the case of a piston and cylinder, or a shaft
and a bearing. The effect is comparatively slow, taking place over a
number of days. The two surfaces must break down gradually, increasing
the friction to a point where motion must cease. Then the mixing
continues until they are welded solidly to each other."

Ordinarily, the dusk of evening would have fallen over the landscape,
but the blaze of the comet now lit the countryside with an unnatural
gold that reflected like a flame through the windows and onto the faces
of the men and boys in the laboratory.

"As to the cause of this phenomenon," Professor Maddox said with an
obviously weary deliberation in his voice, "we can only hope to find an
explanation and a cure before it is too late to do the world any good."

"There can't be any question of that!" said Ken intensely. "The
resources of the whole scientific world will be turned on this one
problem. Every industrial, university, and governmental laboratory will
be working on it. Modern science can certainly lick a thing like this!"

Professor Maddox turned from the window, which he had been facing. A
faint, grim smile touched the corners of his lips and died as he
regarded the boys, especially Ken. His face took on a depth of soberness
Ken seldom saw in his father.

"You think no