seemed loose
when we started work, but as soon as we broke the bearings apart they
seemed to fasten onto the shaft like they were alive. How do you account
for that? The bearings were new; I just cast them yesterday."

"They were contaminated by dust between casting and installation in the
protected room. We've got to dig a lot deeper before we've got the right
answer. It might be worthwhile setting up another rig just like the one
we have in order to get some more juice in our batteries. Do you think
you could do it again, or even several times? That engine lasted about
90 hours, didn't it?"

"Eighty-eight, altogether. I suppose I could do it again if you think
it's worth it. The trouble is getting generators. Maybe we could machine
the shaft of this one and cast a new set of bearings to fit. I'll try if
you think it's worth it."

"Get it ready to run," said Ken. "The battery power for our radio isn't
going to last forever. We'll be in a real jam if we lose touch with the
outside."

Chapter 11. _The Animals Are Sick_

That night, Ken reported to his father the fate of the engine assembled
by Art.

"It did seem too good to be true," said Professor Maddox. He stretched
wearily in the large chair by the feeble heat of the fireplace. "It
bears out our observation of the affinity of the dust for metals."

"How is that?"

"It attaches itself almost like a horde of microscopic magnets. It
literally burrows into the surface of the metal."

"You don't mean that!"

"I do. Its presence breaks down the surface tension, as we had supposed.
The substance actually then works its way into the interstices of the
molecules. As the colloid increases in quantity, its molecules loosen
the bond between the molecules of the metal, giving them increased
freedom of motion.

"This can be aggravated by frictional contacts, and finally we have the
molecular interchange that binds the two pieces into one."

"The only metal that would be clean would be that which had been
hermetically sealed since before the appearance of the comet," said Ken.
"Look--wouldn't this affinity of the dust for metal provide a means of
purifying the atmosphere? If we could run the air through large filters
of metal wool, the dust would be removed!"

"Yes, I'm very sure we could do it that way. It would merely require
that we run the atmosphere of the whole Earth through such a filter. Do
you have any idea how that could be done?"

"It would wor