"What do you mean?"
Frank, in reply, bent over the stem-locker of the aeroplane and drew out what Harry instantly recognized as the silk envelope of an experimental dirigible they had built the year before.
"Now then," said Frank, "give a hand here."
They all three pulled and hauled till the envelope was spread level on the ground, all folds and creases having been carefully shaken out.
"Well," said Harry, "this would carry an awful weight of ivory, but how are you going to inflate it?"
"With these cylinders," was the answer as Frank opened the store-room below the floor of the Golden Eagle and pointed to a dozen cylindrical steel receptacles. "They contain more than enough pure hydrogen gas at a high pressure," he explained, "to inflate the bag."
In his enthusiasm Harry waved his helmet and Ben did the same.
"An aerial express, hurray!"
The inflation hose was soon connected to the first of the cylinders and with a hiss the gas rushed into the bag when a turn of the wrench set free the precious stuff. Slowly the big yellow envelope swelled and assumed shape until by the time the last cylinder was empty it was tugging and straining to rise. But the boys had weighted it down with rocks and pegged its net ropes to the ground.
The ivory was loaded into a sort of rope basket, like those used to hoist cargo aboard a ship, and in a short time, so quickly did they work, they were ready for the air, so far as what Harry called "the airbarge" was concerned.