’Ah, that is another matter which I will explain directly. As I have told you before, the air here is so dense that to make a flying-machine was never a matter of any great difficulty. For the same reason, with a properly constructed pair of wings, you can, after a little practice under expert tuition, very soon learn to soar into the air, and fly about after a fashion. It has, however, hither-to, it must be confessed, been a rather clumsy fashion. Now, this is the first time I have seen it really gracefully and easily done. I knew before we went away that Prince Alondra and his tutor—an old scientist named Amaldo, who was also the king’s tutor when he was a boy—were at work upon some new device which was understood to be the prince’s own idea originally. What it was I never knew exactly, for they kept it a sort of half-secret. Here, however, it seems, is the outcome of the idea; and a very successful outcome too, so far as I can judge.’ ’What is the invention?’ asked practical Jack. ’Does it consist, I mean, in the dress, in the material of which it is composed—wonderful stuff it certainly seems to be—or in a new shape for the wings, or what?’ ’Ah, that is exactly what I do not yet know any more than you. Doubtless, the prince will enlighten us ere long—when he has enjoyed the general mystification a little longer. ’Well, now, to turn to the other point. You say the air here feels to you light and exhilarating rather than dense and heavy. It is not exactly the air which gives you this feeling; it is due rather to the difference in what we call gravity. On Mars, things weigh only half what they would weigh on our Earth. It follows that our muscles feel stronger in proportion. It requires less strength, less exertion, to lift your leg or your arm. Every action or movement, great or small, is easier—even breathing. Therefore, you have a sense of lightness, of ease, of unusual strength.’ A light broke upon Gerald. ’I see! That was why the prince seemed so light to me when I went to help him up just now!’ he cried. ’Exactly. We who have come from Earth, and who possess muscles used to the greater weight of everything there, are all "strong men" here. You will find this one of the first and one of the most curious of your experiences here.’ Just then they saw King Ivanta approaching, bringing Alondra with him. They had left the crowd of richly arrayed courtiers and officers to come across to Gerald. ’Alondra,’ said the king, indicating Gerald as they drew near, ’I wish to commend this brave young gentleman to your especial care; and I hope you two will become good friends. You must teach him to fly. If he learns to fly as well as he has learned to swim, then I can testify that he should make a clever performer; for he saved your father’s life!’ *CHAPTER XIII.* *THE PALACE IN THE CLOUDS.*