On the following 19th of April, seven months after the unexpected return of Uncle Prudent¹ and Phil Evans, Philadelphia was in a state of unwonted excitement. There were neither elections nor meetings this time. The aerostat "Go-Ahead," built by the Weldon Institute, was to take possession of her natural element.  
The celebrated² Harry³ W. Tinder, whose name we mentioned at the beginning of this story, had been engaged as aeronaut. He had no assistant, and the only passengers were to be the president and secretary of the Weldon Institute.
 
Did they not merit such an honor? Did it not come to them appropriately to rise in person to protest against any apparatus⁴ that was heavier than air?
 
During the seven months, however, they had said nothing of their adventures; and even Frycollin had not uttered a whisper of Robur and his wonderful clipper. Probably Uncle Prudent and his friend desired that no question should arise as to the merits of the aeronef, or any other flying machine.
 
Although the "Go-Ahead" might not claim the first place among aerial locomotives, they would have nothing to say about the inventions of other aviators⁵. They believed, and would always believe, that the true atmospheric⁶ vehicle was the aerostat, and that to it alone belonged the future.
 
Besides, he on whom they had been so terribly—and in their idea so justly—avenged, existed no longer. None of those who accompanied him had survived. The secret of the "Albatross" was buried in the depths of the Pacific!
 
That Robur had a retreat, an island in the middle of that vast ocean, where he could put into port, was only a hypothesis; and the colleagues reserved to themselves the right of making inquiries⁷ on the subject later on. The grand experiment which the Weldon Institute had been preparing for so long was at last to take place. The "Go-Ahead" was the most perfect type of what had up to then been invented in aerostatic art—she was what an "Inflexible⁸" or a "Formidable" is in ships of war.
 
She possessed⁹ all the qualities of a good aerostat. Her dimensions allowed of her rising to the greatest height a balloon could attain¹⁰; her impermeability¹¹ enabled her to remain for an indefinite time in the atmosphere; her solidity would defy any dilation¹² of gas or violence of wind or rain; her capacity gave her sufficient ascensional force to lift with all their accessories an electric engine that would communicate to her propellers¹³ a power superior to anything yet obtained. The "Go-Ahead" was of elongated¹⁴ form, so as to facilitate her horizontal displacement¹⁵. Her car was a platform somewhat like that of the balloon used by Krebs and Renard; and it carried all the necessary outfit¹⁶, instruments, cables, grapnels, guide-ropes, etc., and the piles and accumulators for the mechanical power. The car had a screw in front, and a screw and rudder behind. But probably the work done by the machines would be very much less than that done by the machines of the "Albatross."
 
The "Go-Ahead" had been taken to the clearing in Fairmount Park, to the very spot where the aeronef had landed for a few hours.
 
Her ascensional power was due to the very lightest of gaseous¹⁷ bodies. Ordinary lighting¹⁸ gas possesses an elevating force of about 700 grams for every cubic meter. But hydrogen possesses an ascensional force estimated at 1,100 grams per cubic meter. Pure hydrogen prepared according to the method of the celebrated Henry Gifford filled the enormous balloon. And as the capacity of the "Go-Ahead" was 40,000 cubic meters, the ascensional power of the gas she contained was 40,000 multiplied by 1,100 or 44,000 kilograms.
 
On this 29th of April everything was ready. Since eleven o'clock the enormous aerostat had been floating a few feet from the ground ready to rise in mid-air. It was splendid weather and seemed to have been made specially¹⁹ for the experiment, although if the breeze had been stronger the results might have been more conclusive²⁰. There had never been any doubt that a balloon could be guided in a calm atmosphere; but to guide it when the atmosphere is in motion is quite another thing; and it is under such circumstances that the experiment should be tried.
 
But there was no wind today, nor any sign of any. Strange to say, North America on that day omitted to send on to Europe one of those first-class storms which it seems to have in such inexhaustible numbers. A better day could not have been chosen for an aeronautic²¹ experiment.
 
The crowd was immense in Fairmount Park; trains had poured into the Pennsylvania capital sightseers from the neighboring states; industrial and commercial life came to a standstill that the people might troop to the show-master, workmen, women, old men, children, members of Congress, soldiers, magistrates²², reporters, white natives and black natives, all were there. We need not stop to describe the excitement, the unaccountable movements, the sudden pushings, which made the mass heave and swell²³. Nor need we recount the number of cheers which rose from all sides like fireworks when Uncle Prudent and Phil Evans appeared on the platform and hoisted²⁴ the American colors. Need we say that the majority of the crowd had come from afar not so much to see the "Go-Ahead" as to gaze on these............