This sonnet by Percy Shelley was written during a time when there was a craze sweeping through France and England over creating manned hot air balloons. These balloon flights (the oldest human-flying technology, a century before the Wright brothers) represented the reckless adventurousness of the inventors and scientists of the time, who risked their lives to fly these highly volatile and dangerous machines in order to be some of the first humans to see the world from high above, (as well as to achieve fame and glory).
While such scientific explorations using hot air balloons were taking place, Shelley was trying to achieve something else with balloons. A political revolutionary, Shelley launched small handmade balloons filled with his manifesto, “A Declaration of Rights” that espoused many of his radical ideas at the time (e.g. “Government has no rights”; “If a person's religious ideas correspond not with your own, love him nevertheless”; “Man, whatever be his country, has the same rights in one place as another, the rights of universal citizenship”) in hopes that it would instigate social change.
While the balloons were ineffective as a social agitator (or as a mode of transportation), they represented a glimmer of hope and optimism in the sky that is reflected in this poem.
This piece was commissioned and premiered by The New York Virtuoso Singers with Harold Rosenbaum conducting, on Nov. 29, 2015 at the National Sawdust, Brooklyn, NY.

Sonnet: To a Balloon Laden with Knowledge

Bright ball of flame that through the gloom of even Silently takest thine aethereal way,
And with surpassing glory dimm'st each ray Twinkling amid the dark blue depths of Heaven,— Unlike the fire thou bearest, soon shalt thou Fade like a meteor in surrounding gloom, Whilst that, unquenchable, is doomed to glow
A watch-light by the patriot's lonely tomb;
A ray of courage to the oppressed and poor;
A spark, though gleaming on the hovel's hearth, Which through the tyrant's gilded domes shall roar; A beacon in the darkness of the Earth;
A sun which, o'er the renovated scene,
Shall dart like Truth where Falsehood yet has been.