“Dorothy,” said Tom seriously, “I think Jim can go and be perfectly safe. I thought this whole business out, coming over in the boat. Not being completely and totally blind, I foresaw the inevitable occurrence which has inevitably occurred, and I didn’t want to lose Jim for my own sake, as well as my sister’s. I’ve had this on my mind ever since we left Portsmouth. I knew he’d think he ought to go; so as soon as I reached Folkestone I had a little yacht built, a sloop with an auxiliary motor, which hasn’t a nail in her. She’s all wood, rubber and canvas, except the engine, and if the engine disappears there’s a set of rubber valves that instantly closes the shaft hole. ‘The man’ can come right up alongside, stand up and throw waves at her, and she can’t sink. I had a wire from there to-night that she was done. They’ve been working on her twenty-four hours a day since I started her, and she’s a mighty nice little boat. The crew is engaged, and all Jim has to do is take possession.” “That ought to save the boat,” said Dorothy, shaking her head sadly, “but how can you save Jim from the fate of Dr. Heidenmuller, or of the men on the battleships who died as he did?” “You never did have much opinion of my brains, Dorothy,” said Tom. “Don’t you suppose I thought of the effect those waves would have? You know none of the other ships in Portsmouth harbor were injured, when the German ship disappeared. That proves that the man has some way of directing his waves. So he may not hurt Jim at all. But I didn’t take any chances on that. I’ve had a cage of caema built over the cockpit, and everything is arranged so that the boat can be run without going outside that cage.” Dorothy heaved a sigh of relief. She bent forward and kissed Tom in the full face of the assembly. “Tom, you’re the finest, best man in the world, except one.” “That’s it,” said Tom with a grin. “Second place for old uncle Thomas now.” “But Tom,” I said, “I follow the boat construction all right, but for Heaven’s sake what is this caema that I’ve heard so much about, and what’s the use of the cage?” “Oh, I forgot you might not understand that,” said Tom. “You know, or you ought to know, it’s in every school physics, that if you put a cage of a conductor like copper around any instrument which is easily affected by any electrical discharge, the electrical waves spread out, follow the surface of the cage, and don’t penetrate the interior. The instrument is wholly unaffected. Well, caema is the newest organic conductor. It acts the same way with any radio-active waves. They spread out all over it, and can’t get through. I’ve had a cage built of it to insulate you and everything else that’s inside.” “Why wouldn’t it work around the battleships then?” I asked. “Because the battleships are made of steel; and if you put a cage like that around them, they could hardly move. It only worked on your boat because it’s wood outside.”