"No; Jack and I were only having a red-hot discussion about diamonds on the moon," said Mark, with a laugh.

"Diamonds on the moon!" exclaimed Professor Henderson.

"Diamonds on the moon?" repeated his friend, Prof. Santell Roumann. "Is this a joke, boys?"

"Mark thinks so, but I don't!" cried Jack, enthusiastically. "Look here, Professor Henderson, and also Mr. Roumann. Here is one of the newspapers that we brought back with us in our projectile, the Annihilator, after our trip to Mars. I have been translating some of the articles in it, and to-night I came across one that told of a trip made by some of the inhabitants of Mars to the moon, in a sort of projectile, like ours, only more on the design of an aeroplane.

"They landed on the moon, the article states, and found a big field, or deposit, of Reonaris, which I claim are diamonds. Mark says I'm wrong, but, Professor Henderson, isn't Reonaris to the Martians what diamonds are to us?"

"It certainly is," agreed the older scientist, and he looked for confirmation to his scholarly companion.

"Reonaris is substantially a diamond," said Professor Roumann. "It has the same chemical constitution, and also the diamond's hardness and brilliancy. But I don't understand how any diamonds can be on the moon."

"You can read this for yourself," suggested Jack, passing over the paper, which was one of some souvenirs brought back from what was the longest journey on record, ever taken by human beings.

Mr. Roumann adjusted his glasses, and carefully read the article that was printed in such strange characters. As he perused it, he nodded his head thoughtfully from time to time. Then he passed the paper to Professor Henderson.

The older scientist was somewhat longer in going over the article, but when he had finished, he looked at the two boys, and said: "Jack is right! This is an account of a trip made to the moon by some of the Martians, who have advanced much further in the art of air navigation than have we. Some of the words I am not altogether familiar with, but in the main, that is what the paper states."