Up and down these the professor, the boys and Andy went, taking in
tools and materials, and removing considerable refuse which had
accumulated during the building of the craft.

Finally all was in readiness for starting the making of the gas. The
ship was not wholly complete and no supplies or provisions for the
long voyage had been taken aboard. The Flying Mermaid was about a ton
lighter than it would be when fully fitted out, but to make up for
this the professor had left in the ship a lot of tools and surplus
machinery so that the craft held as much weight as it would under
normal conditions. If the gas lifted it now it would at any other
time.

"Start the generator," said Mr. Henderson, to Mark. "We'll soon see
whether we are going to succeed or fail."

The boy turned a number of levers and wheels. The machine which made
the powerful vapor was soon in operation. The professor had already
added enough of the secret compound to the tank containing the other
ingredients, and the big pump was sucking in air to be transformed
into the lifting gas.

The boys and the professor were in the engine room. Andy Sudds, with
Bill and Tom, had taken their places in the living room, to more
evenly balance the ship, since the things in it were not yet all in
their proper places. As for Washington he was busy running from the
shed to the ship with various tools and bits of machinery the
professor desired.

The gas was being generated rapidly. Throughout the ship there