Tom put his craft through a number of evolutions, and when he found that she was in perfect control as an aeroplane, he started the gas machine, filled the big black bag overhead, and, when it was sufficiently buoyant, he shut off the motor, and the Black Hawk floated along like a balloon.

“That’s what we’ll do if our power happens to give out when we get over an African jungle, with a whole lot of wild elephants down below, and a forest full of the red pygmies waiting for us,” explained Tom to Mr. Durban.

“And I guess you’ll need to do it, too,” answered the hunter.  “I don’t know which I fear worse, the bad elephants wild with rage, as they get some times, or the little red men who are as strong as gorillas, and as savage as wolves.  It would be all up with us if we got into their hands.  But I think this airship will be just what we need in Africa.  I’d have been able to get out of many a tight place if I had had one on my last trip.”

While the Black Hawk hung thus, up the air, not moving, save as the wind blew her, Tom with his father and Mr. Jackson made an inspection of the machinery to find out whether it had been strained any.  They found that it had worked perfectly, and soon the craft was in motion again, her nose this time being pointed toward the earth.  Tom let out some of the gas, and soon the airship was on the ground in front of the shed she had so recently left.

“She’s all right,” decided the young inventor after a careful inspection.  “I’ll give her a couple more trials, put on the finishing touches and then we’ll be ready for our trip to Africa.  Have you got everything arranged to go, Ned?”

“Sure.  I have a leave of absence from the bank, thanks to your father and Mr. Damon, most of my clothes are packed, I’ve bought a gun and I’ve got a lot of quinine in case I get a fever.”

“Good!” cried the elephant hunter.  “You’ll do all right, I reckon.  I’m glad I met you young fellows.  Well, I’ve lived through my first trip in the air, which is more than I expected when I started.”

They discussed their plans at some length, for, now that the airship had proved all that they had hoped for, it would not be long ere they were under way.  In the days that followed Tom put the finishing touches on the craft, arranged to have it packed up for shipment, and spent some time practicing with his electric rifle.  He got to be an expert shot, and Mr. Durban, who was a wonder with the ordinary rifle, praised the young inventor highly.

“There won’t many of the big tuskers get away from you, Tom Swift,” he said.  “And that reminds me, I got a letter the other day, from the firm I collect ivory for, stating that the price had risen because of a scarcity, and urging me to hurry back to Africa and get all I could.  It seems that war has broken out among some of the central African tribes, and they are journeying about in the jungle, on the war path here and there, and have driven the elephants into the very deepest wilds, where the ordinary hunters can’t get at them.”