the mechanism.

"You'd better hold your horses there," said Arcot. "If you take that off
now, we sure will need the _Ancient Mariner_ to catch up with it. It
will produce an acceleration that no man could ever stand--something on
the order of five thousand gravities, if the tubes could stand it. And
since that one is equipped with the invisibility apparatus, you'd be out
one good invisibility suit. Restrain yourself, boy, and I'll go get a
new knob control.

"Wade, get the boy a rock to hold him down. Better tie it around his
neck so he won't forget it and fly off into space again. It's a nuisance
locating so small an object in space and I promised his father I'd bring
the body back if there was anything left of it." He released Morey as
Wade handed him a large stone.

A few minutes later, he returned with a new adjustment dial and repaired
Morey's apparatus. The strain was released when he turned it, and Morey
parted with the rock with relief.

Morey grunted in relief, and looked at the offending pack.

"You know, that being stuck with a sky-bound gadget that you can't turn
off is the nastiest combination of feeling stupid, helpless, comical,
silly and scared I've hit yet. It now--somewhat late--occurs to me that
this is powered with a standard power coil, straight off the production
line, and that it has a standard overload cut-out for protection of
associated equipment. I want to install an emergency cutoff switch, in
case a knob, or something else, goes sour. But I want to have the
emergency overload where I can decide whether or not an emergency
overload is to be accepted. I'd feel a sight more than silly if that
overload relay popped while I was a couple thousand feet up.

"Trouble with all this new stuff of ours is that we simply haven't had
time to find out all the 'I never thought of that' things that can go
wrong. If the grid resistor on that oscillator went out, for instance,
what would it do?"

Arcot cocked an eye at the power pack, visualizing the circuits. "Full
blast, straight up, and no control. But modern printed resistors don't
fail."

"That's what it says in all the books." Wade nodded wisely. "And you
should see the stock of replacement units every electronics shop stocks
for purposes of replacing infallible units, too. You've got a point, my
friend."

"I can see four ways we can change these things to fail-safe operation,
if we add Morey's emergency cut-off switch. If it did go on-full th