"Good!" ejaculated Whittinghame. "Left Naocuanha at seven? She has a thousand mile flight. Allowing her speed to be the same as that of the 'Meteor'—although I doubt it—she ought to reach Salto Augusto by about noon or one o'clock. They couldn't have chosen a better time as far as we are concerned, for the sun will be almost directly overhead. At five thousand feet we'll run no risk of being spotted."
At exactly fifteen minutes past twelve the watchers on the British airship saw her rival approaching. The "Libertad" was flying low—at an altitude of about five hundred feet. This proved that her speed was approximately the same as that of her opponent. In appearance she strongly resembled the "Meteor," but, of course, Whittinghame was not aware of the details of her construction and propulsive arrangements. Durango had had the secret of the ultra-hydrogen, but whether he knew how to render the gas non-inflammable was a question that could not be satisfactorily answered by the Captain of the "Meteor."
Keeping the "Libertad" under observation by means of their powerful binoculars the officers of the "Meteor" saw the Valderian craft alight at less than half a mile from the outskirts of the town. She did not remain long. Almost skimming along the ground, like a snake crawling stealthily through the grass, she turned westward.
Although the "Meteor" could not adopt offensive methods over Brazilian territory, there was now no further need of concealment. She could follow the "Libertad" relentlessly, keeping her in view until she crossed the border. Then she would act promptly and decisively.
Swooping downwards, but still maintaining a superior elevation, the "Meteor" began to chase. With her motors running "all out" she slowly yet surely overhauled her prey, till a sudden spurt on the part of the "Libertad" announced the fact that she had sighted her pursuer, and was putting on extra speed.
Mile after mile the two airships tore at a terrific rate. On board the "Meteor" the bomb-dropping gear was made ready, and the light quick-firers manned. But even had Whittinghame wished to open fire upon the enemy, the speed at which the "Meteor" was travelling put that out of the question, until the "Libertad" was overhauled sufficiently for the British craft's guns to be trained abeam. Nor could the machine guns on the promenade deck be worked. No man could stand to serve them in the howling gale that swept past the rapidly moving vessel.
On the other hand Durango could make use of the two after guns on the "Libertad" without risk. To open the bow-ports of the "Meteor" meant serious damage both to the structure of the hull and to her crew, unless the speed were materially reduced.
The Captain of the "Libertad" cared not one jot for international rights now that he was on his way back to Valderia. He opened fire upon the "Meteor," two shells fitted with time-fuses screeching past the huge flimsy target and bursting three hundred yards astern.
"This won't do," remarked Whittinghame calmly. "We cannot afford to be potted without chance of replying."
He turned and gave a brief order. The elevating planes and an addition of ultra-hydrogen resulted in the "Meteor" quickly bouncing up another two thousand feet. Her Captain's plan was to gain an important advantage in altitude and continue to overhaul the "Libertad." He would thus have what corresponded to the weather-gauge in old-time frigate actions.