Suspended from a hook directly over the bench was a beautiful six-foot model of a racy-looking monoplane of peculiar and striking design. It was glistening in several coats of spar-varnish, and so light and delicate was its spidery frame that, as John reached out to take it in his hand, the exhalation of his breath set it swaying away from him. "My word, it's a light boy all right!" exclaimed John admiringly, as he carefully took hold of the pretty thing. "That's just the feature we've tried to get, too, Buddy,--lightness." He looked closely at the long, graceful pair of wings, which were of an unusual thickness and a slight upward thrust like those of a bird, and which widened batlike as they ran back and joined the rear fuselage or body of the craft. "Have you put the helium-gas in these wings yet, Paul, as we planned? I see you have installed the valves. There's a valve in the after-fuselage, too." "The wings and fuselage are both filled," said Paul; "that is what makes the Sky-Bird so light. If you had brought more helium the last time you were here, I could have pumped in twice the quantity, I think, and that would have made her so light she would rise of her own accord, I really believe. As it is, she now weighs less than a half-ounce. I had the scales on her yesterday." John shared his brother's enthusiasm. "Fine!" he cried, with sparkling eyes. "Why, that's almost a neutral condition, as she is! Buddy, if we can apply this principle to a full-size machine--and I don't know why we can't--we shall have solved the biggest problem facing airplane designers to-day. With a machine weighing only a trifle more than her load of fuel and baggage, she will not only fly a lot faster but go a lot farther, with a given supply of fuel, than the present-day planes. And what is more, she could attain good speed with a single engine of reasonable power, where now many machines are handicapped with the burdensome weight of an extra power-plant. When will she be ready to test out?" "I had planned to give her a trial in the old fair-grounds Saturday afternoon," said Paul. "I've asked Bob Giddings to go along." "That's all right; Bob is a fine lad," said John; "but since you have set the trial for Saturday afternoon, and Bob's father is usually at home at that time, why don't you ask him to view the affair also? I'm sure he would enjoy it. He's a great sportsman, you know, like most newspaper men, and considerably interested in aeronautics." "I had not thought of it; I'll do it," was the prompt response of Paul. "But we must warn him to silence, John. Whatever happens, we don't wish this to get into the _Daily Independent_."