After a desperate journey Tom and his friends reached civilization, with a large supply of gold.  Tom regretted very much the destruction of the airship, but he at once set to work on another—­a monoplane this time, instead of a combined aeroplane and dirigible balloon.  This new craft he called the Humming Bird and it was a “sky racer” of terrific speed.  In it, as we have said, Tom brought a specialist to operate on his father, when, because of a broken railroad bridge, the physician could not otherwise have gotten to Shopton.  He and Tom traveled through the air at the rate of over one hundred miles an hour.  Later, Tom took part in a big race for a ten-thousand-dollar prize, and won, defeating Andy Foger, and a number of well-known “bird-men” who used biplanes and monoplanes of a more or less familiar type.

The government became interested in Tom’s craft, the Humming Bird, and, as told in the ninth book of this series, Tom Swift and His Sky Racer, they secured some rights in the invention.

And now Tom, who had done nothing for several months following the great race—­that is, nothing save to work on his new rifle—­Tom, we say, sighed for new adventures.

“Well, Tom, what is on your mind?” asked his father at the supper table that evening.  “What is worrying you?”

“Nothing is worrying me, Dad.”

“You are thinking of something.  I can see that.  Are you afraid your electric rifle won’t work as well as you hope, when Ned comes over to try it?”

“No, it isn’t that, Dad.  But I may as well tell you, I guess.  I’ve been reading in the paper about a big elephant hunt in Africa, and I—­”

“That’s enough, Tom!  You needn’t say any more,” interrupted Mr. Swift.  “I can see which way the wind is blowing.  You want to go to Africa with your new rifle.”

“Well, Dad, not exactly—­that is—­”

“Now, Tom, you needn’t deny it,” and Mr. Swift laughed.  “Well, I don’t blame you a bit.  You have been rather idle of late.”

“I would like to go, Dad,” admitted the young inventor, “only I’d never think of it while you weren’t well.”

“Don’t worry about me, Tom.  Of course I will be lonesome while you are gone, but don’t let that stand in the way.  If you want to go to Africa, you may start to-morrow, and take your new rifle with you.”

“The rifle part would be all right, Dad, but if I went I’d want to take an airship along, and it will take me some little time to finish the Black Hawk, as I have named my new craft.”

“Well, there’s no special hurry, is there?” asked Mr. Swift.  “The elephants in Africa are likely to stay there for some time.  If you want to go, why don’t you get right to work on the Black Hawk and make the trip?  I’d like to go myself.”

“I wish you would, Dad,” exclaimed Tom eagerly.

“No, son, I couldn’t think of it.  I want to stay here and get well.  Then I am going to resume work on my wireless motor.  Perhaps I’ll have it finished when you come back from Africa with an airship load of elephants’ tusks.”