"You'll go, too, won't you, Mark?" asked Jack.

"Oh, I'm not going to be left behind. I'll go if the rest do, but I
don't believe you'll find any diamonds on the moon. If there ever were
any, the Martians took them." For Mark had been partly convinced after
the confirmation by the two professors of Jack's translation.

"I'll take a chance on the sparklers," said his chum. "But now, let's
go into details, and figure out when we can start. It ought not to take
very long to get ready."

As has been explained in detail in the other books of this series,
Professor Amos Henderson and the two lads, Mark Sampson and Jack
Darrow, had undertaken many strange voyages together. Sometimes they
were accompanied by friends and assistants, while Washington White, a
sort of servant, helper, and man-of-all-work, and Andy Sudds, an old
hunter, always went with them.

Mark and Jack were orphans, who had been adopted by Professor
Henderson, who spent all his time making wonderful machines for
transportation, or conducting strange experiments.

The two boys had been rescued by Professor Henderson and Washington
White from a train wreck. Although both boys were badly hurt, they were
nursed back to health by the eminent scientist, who soon learned to
care for the lads as though they had been his own sons.

They aided the professor, as soon as they were able, in constructing an
airship, called the _Electric Monarch_, in which Professor Henderson
hoped to be able to reach the North Pole. The boys thoroughly enjoyed