I admire The Aeronauts for its purity. This not a movie that does anything. It's a movie that seems to exist because somewhere along the line, a producer or writer or director (here, Tom Harper is all three, which means it's probably safe to blame him) heard about how 19th Century scientists figured out a great deal of what we now know of the structure of the Earth's atmosphere by riding to spectacularly dangerous heights in hot-air balloons, and thought, "well, that's pretty interesting!" And then made an entire movie designed to tell us about these scientists and these hot-air balloons, so we would also think that it was all pretty interesting. Which, to be fair, it is. Just not, maybe, interesting as a movie. At least, not interesting as this movie.

The Aeronauts starts in 1862, with Amelia Wren (Felicity Jones) running late, and James Glaisher (Eddie Redmayne) fretting about this (Glaisher was a real man who really went on balloon missions; this film presents a composite of his life's work). For James is a scientist - a weather scientist, I almost put, except the whole point is that weather science doesn't exist yet - who will be riding up as high as a hot-air balloon can take him, and Amelia is the balloon pilot who will bring him there, and the crowd gathered to watch the spectacle is growing vocally angry with her conspicuous absence. This immediately gives way to enthusiasm and celebration when she finally shows up, demonstrating how well she knows how to play to an audience: she's dressed in a lime green thing, and she's waving a dog all around, making a big show of finding it more interesting than her harrumphing scientist passenger. Note that Amelia's talent for showmanship will immediately cease to be a plot point. It's just there - I cannot say why. But then again, "it's just there - I cannot say why" describes a great many of the events in this movie and frankly, the movie itself. So it's all good, I guess.

Once the balloon takes off, The Aeronauts starts to split its attention between two plot threads: first, what happens to Amelia and James on their roughly 90-minute flight up and back down, during which they explode the record for highest altitude reached by humans, and also learn to their enormous dismay that the air gets very cold and very thin when you're seven miles up into it. Second are flashbacks to the story of how James declared to his harrumphing scientist colleagues - much harrumphing in this movie, there is - that he would go on this balloon ride and run these tests and in so doing invent the science of weather prediction, and how this involved talking Amelia out of retirement, after a very horrible flight gone wrong some time later. Which is presented within its own flashbacks, though I cannot at this point recall if the flashbacks are nested inside of each other.

The very simple way to break the movie down, and luckily it is also accurate, is that the scenes in the balloon are generally at least okay, and a couple of them are really quite good, whereas the scenes in flashback range from boring to very boring. At least, when it's in the sky, the film can offer the thrill of watching two people trying to survive in extreme conditions, and the one truly inspired moment in the whole film finds Harper and cinematographer George Steel switching over to fish-eye lenses to create a hideous distortion inside the basket of the balloon, as the increasingly confused James and the only-slightly-more-stable Amelia try to cope with their failing perceptual organs as they run out of breathable oxygen (the film doubles-down, effectively, by also filtering the audio to sound fuzzy and murky). It has some exciting moments, that is to say, and some very beautiful moments as well: the film's CGI representation of the sky above thick clouds has a rich, majestic look, and if nothing else, the film understands how to play with scale.

There's unfortunately still the matter of Jones and Redmayne, teaming back up five years later to rekindle their damp chemistry from The Theory of Everything. The Aeronauts leaves romance out, which helps both actors; they can focus more on their characters' fussy idiosyncrasies without having to make cow eyes at each other on top of it. But Redmayne, in particularly, is pinioned by how perfectly uninteresting his character is: James is an enthusiastic nerd, and while that's something Redmayne can do without trying at this point, there's simply not room to anything other than exist as a meat puppet in a wicker box. Jones has more to do by far, with Amelia's guilt-ridden past allowing her to at least look stricken and sad, but neither the writing nor the acting supports any of the shifts in mood that the character undergoes throughout the movie. She's not quite as purely functional as her co-star, but for all the film's efforts to make this a character story, they don't take.

Ah yes, all those efforts. Slightly less than half of the film's 100 minutes are devoted to the Amelia and James's lives in the run-up to the flight itself, and I think it's fair to suggest that they are wholly and irredeemably boring. Simply put, the movie has already completely answered one of the two questions driving this material - will James find the means to launch his controversial mission? - and has partially answered the other - will Amelia find the fortitude to go on another flight, and will she freak out when miles in the sky? So watching the slow, mid-Victorian social bargaining that goes into all of the scenes on the ground is the most dreary grind imaginable. Not helping matters, the film has devoted most of its spectacle budget to the balloon flights, so it's pretty much stock British-produced costume drama imagery throughout: a lot of glumly lit wood-paneled interiors, as though the filmmakers hoped that the mere fact of dark lighting would cast a kind of prestige on the standard-issue set design and costumes.

The flashbacks are thus not dramatically necessary, nor pleasurable to watch in their own right; they also don't tell us much of anything about the characters, which is really the only reason they're present. Most of what matters gets discussed up in the balloon, anyway, which is the only place the film carves out anything like a specific identity. And even then, far too much of the identity is based in historical trivia that's presented in a somewhat mangled way, with over-dramatic music and showy visual effects smothering the nuts-and-bolts of the science experiments. The great Roger Ebert once wrote, "good movies rarely contain a hot-air balloon," and The Aeronauts, which contains very little else, is a particularly grim proof of his philosophy.