Finally Mr. Durban suggested that they erect improvised shelters, behind which they could stand with their rifle, and breastworks were made out of packing boxes.  Then our friends were comparatively safe.  But they had to be on the alert, and it was nervous work, for they could not tell what minute the blacks would rush from the jungle, and, in spite of the fire from the electric rifle and other guns, overwhelm the ship.

It was very trying to Tom and Ned, for they had to work hard and rapidly in the close engine room.  The sweat dripped down off them, but they kept at it.  It was three hours before the broken cylinder was removed, and it was no light task to put in the other, for the valves had to be made very tight to prevent leakage.

The two lads stopped to get something to eat, while the guards kept sharp watch against a surprise.  At intervals came a flight of barbs, and occasionally a black form could be seen, when it was instantly fired at.  Several times the barbaric noise of the tom-toms and war drums, with which the shouts of the natives mingled, broke out deafeningly.

“Think you can repair it by night?” asked Mr. Durban anxiously of Tom.

“I hope so,” was the response.

“Because if we have to stay here after dark—­well, I don’t want to do it if I can help it,” finished the hunter.

Neither did the young inventor, and he redoubled his efforts to make the repairs.  It was getting dark when the last belt was in place, and it was high time, too, for the natives were getting bolder, creeping up through the forest to within shooting distance with their arrows and spears.

“There!” cried Tom at length.  “Now we’ll see if she works!” Once more he pulled the starting lever, and this time there was the welcome hiss of the gas.

“Hurrah!” cried Ned.

The young inventor turned the machine on at full power.  In a few minutes the Black Hawk trembled through her length.

“She’s going up!  Bless my balloon basket!  She’s going up!” cried Mr. Damon.

The natives must have suspected that something unusual was going on, for they made a sudden rush, yelling and beating their drums.  Mr. Durban and the others hurried out on deck and fired at them, but there vas little more need.  With a bound the airship left the earth, being rapidly carried up by the gas.  The blacks sent a final shower of spears after her, but only one was effective, slightly wounding the German.  Then Tom started the motor, the propellers whizzed, and the Black Hawk was once more under way, just as night settled over the jungle, and upon the horde of black and howling savages that rushed around, maddened over the escape of their intended victims.

No further accidents marred the trip to the coast, which was reached in due time, and very glad our friends were to be away from the jungle and the land of the red pygmies.

A division was made of the ivory, and Tom’s share was large enough to provide him with a substantial amount.  Ned and Mr. Damon were also given a goodly sum from the sale of the tusks.  The big ones, from the “rogue,” were shipped to the man who had commissioned Mr. Durban to secure them for him.