"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."