"She's certainly a swifter craft than the Hawk," remarked Ferral.
"I will improve the Hawk for you," said Jerrold, "so she will be just as swift as the Eagle."
"Oof ve efer ged der Hawk pack, vich ve don'd know," struck in Carl.
"The biggest trouble with air ships equipped with gasoline," continued Jerrold, "is the fact that the slightest change in the temperature affects the buoyancy. Even a cloud over the sun will cause the gas to contract, and the difference in heat thrown off by the sun at morning and noon will expand the gas and also disturb the equilibrium. Now I have an improvement that remedies that. It consists of a smaller bag inside the gas bag, filled with a vapor of my own invention. When the buoyancy of the outer bag decreases, that of the inner bag increases, and _vice versa_. That gives us a unit of buoyancy which is always the same, and leaves the propeller free to carry us in any direction."
"Greadt!" cried Carl. "I don'd ondershtand vat you vas gedding ad, aber I bed it vas somet'ing fine. Ach!" and he looked downward, "here ve go ofer der lake. I hope dere iss some ships all along der vay, so dot oof anyt'ing habbens ve can trop down ondo vone oof dem."
"Don't worry about our dropping into the water, Carl," smiled Jerrold, "for there is absolutely no danger of that."
In an hour the Eagle was out of sight of land. The sails of one or two schooners could be seen far away on the horizon, but they were too far off to be considered "company."
As the Eagle plowed on and on through the sunny air, with never a hitch or a sign of anything going wrong, Carl's fears slowly subsided and he took delight in this novel experience of crossing a large body of water.
For a time, Matt relieved Jerrold at the motor. So far as the young motorist could see, the Eagle handled as easily as the Hawk; besides that, there were points of superiority about her, in addition to speed, as compared with the Brady air ship.
For three hours the Eagle was over the lake, and then Ferral, with a shout, announced:
"Land ho, messmates, right under our fore foot!"
Harris examined the shore line, critically. A little later, when they were nearer, he turned to Jerrold.
"We're a bit south of Grand Haven," said he, "about two miles, I should judge. I can see the cottages on the trolley line that follows the lake shore."