"What's the matter?" asked his chum.

"That plate remover! Don't you remember you and I had it when we were
fixing the pipes outside the projectile, when we had the other
breakdown? We must have left it back there on the ground."

Jack and his chum gazed blankly at each other.

"I guess we did," admitted Mark dubiously.

"And it is the only one we have," said Mr. Roumann. "We need it very
much, too, for the projectile can't very well be moved without it."

"How can we get it?" asked Jack. "I'm sorry. It was my fault."

"It was as much mine as yours," asserted Mark. "I guess it's up to us
to go back after it. It isn't far. We can easily walk it."

There seemed to be nothing else to do, and, after some discussion, it
was decided to have the two boys walk back after the missing tool,
which was a very valuable one.

"Take fresh life-torches with you," advised Mr. Henderson, "and you had
better carry some food with you. It may be farther back than you think,
and you may get hungry."

"I guess it will be a good thing to take some lunch along," admitted
Jack. "And some water, too. We can't get a drink here unless we come to
a spring, and we haven't seen any since we arrived."