The Martians were hurrying their preparations to blow up the projectile. Perhaps they guessed that they must act promptly, or they may have had an intimation that something was going to happen, when the ports of the electric cannons were closed.

The shutter of the observation tower was sealed, all openings were well fastened, and, just as the mine was completed and the explosive was about to be put in, Mr. Roumann started the atmospheric motor, and the projectile left Mars with a rush.

Of course, the travelers could not see the blank looks of astonishment on the great faces of the Martians, but they could imagine them, as they shot away from the queer little planet at the rate of sixty miles a second.

"Well," remarked Mr. Roumann as he went to the pilot house, after seeing that the motor was working well, "we got to the place we set out for, and we secured some Cardite, which is what I wanted.

I am now able to repay you for building this projectile, Professor Henderson, you need never worry about money again."

"I'm glad of it, as I shall devote the remainder of my life to science, and I may write a book about Mars."

"Well, ob all de transmigatoriousness dat I eber seed," exclaimed Washington, "de continual exteriorosity ob de inhabitants ob dat planetary sphere am de mostest indisputatious!" Though what he meant by that no one knew. But it seemed to give the colored man great satisfaction.

In due time they pa.s.sed beyond the limits of the atmosphere of Mars, and again were sailing through s.p.a.ce, the Etherium motor doing good work. Mr. Roumann tried some Cardite in it, and their speed was increased by half, so they reached the atmosphere of the earth in much shorter time than they calculated.

They met with no mishaps, though they narrowly escaped collision with a great meteorite that was rushing through s.p.a.ce, white hot.

"Well, in a few days we will be at home," remarked Mr. Roumann one night, as he set the atmospheric motor in operation. "And I must say I have greatly enjoyed the trip."

"So have I," admitted Jack, and Mark agreed with him.

"Maybe mah Shanghai rooster won't be glad t' git on terra cotta again," spoke Washington. "I'se glad I didn't let him out on Mars. Dem funny fellers might 'a' eat him up."

The rooster crowed as if glad to be nearing the earth.

Three days later they came in sight of their own planet, but as night came on, and they did not want to land in the dark, the projectile was kept up above until daylight, and a day later a landing was made near the machine shed where the Annihilator had been built.

"Well, here we are, safe home again," said Mark.

"All but the crazy machinist," added Jack. "I hope he likes it up there among the Martians."

"I wonder if we'll ever take another trip like this?" asked Andy.

"Perhaps, some day," replied Mr. Roumann.

"I have some other ideas regarding distant planets that I would like to prove. But we'll take a rest, and see what use we can make of the Cardite. I would also like to learn if my enemy, Forker, sent that crazy machinist to bother me," but he never found out.

As the German had predicted, the red material brought back was enormously valuable, and the projectile was more than paid for by a small part of it. The boys resumed their studies at school, and Professor Henderson devoted much of his time to writing a book describing some of the peculiar conditions on Mars, while Mr. Roumann invented a new motor to run with Cardite, he having revealed the secret of the Etherium one to Professor Henderson.

As for Washington White, he is learning new big words, while Andy says he is glad to be back on a world where a bullet is a bullet and a gun a gun.

THE END