The trip from Canterlot to Ponyville is about four hours long by air; Twilight has not been successful in occupying the first thirty minutes. She had enough time to read through Celestia's letter a few more times, enough to accidentally memorize it, but she has grown bored, and sometimes even she recognizes when a compulsion isn't healthy for her. Spike is napping, catching up on the sleep they missed from getting up so early, but she's too agitated to even try. She decides she wants to practice a little magic.
The chariot is flying at a pretty constant speed, fast enough to create a fairly chilling breeze through the passenger car, so it would be hard to do anything with fire magic. Wind magic would most likely just be stifled by the ambient gale. A barrier could be dangerous, because it would require constant force to remain steady in the wind, and if she loses control and it's anywhere in front of her, she's liable to smack herself in the face. She could practice metrics or metamagic, but it's not every day she's exposed to wind this strong. Casting in those fields wouldn't be much different than on the ground. Surely there's something interesting to do that capitalizes on the novelty of the scene...
She starts reciting the fields of magic in her head. Animation, projection, conjuration, vivification, abstraction... infusion! Most of her recent infusion practice has been wind magic practice as well, so an idea springs into her mind: maybe the natural wind is similar enough to a wind spell to capture it in an amulet; there's one way to find out. Her suitcase magically unzips, and she rummages through it, retrieving a modest emerald and a gold amulet with an empty cavity in the center for the stone. These are standard infusion supplies, jewelry being the go-to medium for persistent or stored magical effects. The highly regular crystalline structure of gemstones captures magic extraordinarily well in comparison to something compositionally erratic like stone or wood, and if you have made such a spellstone, you may as well put it around your neck or horn.
Typically she carries just one gem on her pony, since they're a hassle to maintain. It's a small topaz set into modest gold necklace, infused with an autotargeted vivification spell triggered by a magic flux metric. When a pony tries to cast a spell, either she has enough magic or she doesn't; there's little-to-no feedback on how much magic she has left, only whether it's enough. But if Twilight vivifies magic into the gem, it will immediately reflect (nearly) the same amount back at her. It's coded to work with only her own MR frequency spectrum. This means she can send increasingly stronger bursts, and when one fails, she has an upper bound on her magic reserve. The reflection coefficient diminishes as the day goes on, so she refreshes it every morning.
There's something alluring about having distilled thaumic power close-at-hoof. Twilight often slips into fantasies about being the kind of mare who could dispense any threat with ease, just by activating the right gem on her pony. Those gems are stored on ornate bangles and headdresses and lockets, and are arranged in a technicolor rainbows representing the full spectrum of magical function. She single-hoofedly extinguishes forest fires, reconstructs fallen bridges, incinerates rabid timberwolves, pinpoints rare flowers for antidotes, erects earthquake-resistant shelters with just a day's warning... In the wake of every hardship, duplicate gems automagically float from her space-warping satchel to replace those expended. She answers to nopony, to nothing except goodness and truth. She saves ponies because nopony else can. An eidolon conjuring wild abilities as needed, defender of ponykind, savior of the waking world.
Of course, there are problems with that insane reverie. For one, infused gems lose strength over time if not activated (the Inertial Decay Problem), and a majority of intense spells are medium-destructive when released anyway. Those issues make prohibitive such an extravagant collection, and Twilight doesn't even have much talent for infusion anyway. And even if she could be exactly as powerful and skilled as she fancies, nopony can be everywhere at once. But it doesn't really matter to Twilight. Everypony has a story they like to tell.
She shakes her head a fraction and looks down at the materials in her hooves. Right. It's fairly straightforward to absorb a magical gust into a gemstone, but she hasn't heard of anyone trying to capture a natural phenomenon. It's even a bit more novel than that, since the wind only exists in her own reference frame, although she doubts that will be a complication. First, she has to force her infusion spell to recognize the current as magical, else it won't see anything to bind to the emerald. That could be done in a couple ways: she could try simply infusing the wind with something (say, a glow, or a cooling spell), but she doesn't want to capture magically enhanced wind. A magically inert object won't accept a magic vivification, so that's a non-starter.
Hmm. What would happen if she infused the wind with a metric? Typically, a metric reports its measurements or classifications to the caster, be it a unicorn or whatever sequence or combination it's a subspell of. She predicts that this would end up with the metric reporting to the wind itself, and Celestia only knows what the wind would do with the information. Infusing with a pure metric is a simple enough idea that somepony must have tried it, but she doesn't know who. Until she lands and makes her way to a library to check, she can almost let herself believe she'll the first.
In theory, the wind will be considered magical after the infusion, even though all it's doing is throwing away information. So, in theory, that would allow the infusion spell to target it and, in theory, charge itself with wind magic. Disappointingly, the wind it emits would probably then be indistinguishable from ordinary magic wind. She briefly considers a metric to detect metrics, but her head begins to hurt. Either way, the acquisition of natural "pseudo-magic" would be very interesting indeed. There are a lot of things that could surprise her along the way, but it's worth a shot.
She will need a barrier, after all, so she'd want to put it above her. That way, she won't be in danger from behind it, but she won't block the wind from in front of it. It'll be in the shape of a tube, with the stern end solid. The bow end will be wind-permeable, but set to infuse incident matter with a metric. She'll let in run for a couple seconds, then target the emerald with an infusion.
She spends a bit of time thinking about whether any one metric might make more sense than another, but she can't see it mattering. She decides to go with the simplest one she can think of: report whether there is anything within 1 hoofstep of you. Normally, there would be an exclusion for the target of the metric, so it won't give constant, useless feedback, but she'll omit that, so that it will return a continuous stream of truth. The whole experiment will be fairly taxing, so the metric should be as efficient as possible.
She raises her forehooves into the air to get a rough feel for the wind speed, and can't help to crack a smile at her idea. In her peripheral vision, she notices the royal guard pegasus at her 4-o'clock give her a confused glance, shrug to himself, then refocus his attention on flight. That's okay; she doesn't have to explain. She turns around, lies down on her back, head pointing towards the front of the carriage, and gets to work.
It simply doesn't work.
She spends a long time building up confidence in her ability to maintain the projected tube relatively steady before she dared to actually put the emerald in it, so long that they've almost arrived by the time she actually carries out the steps. She only has enough time to try the full sequence twice. She'll try again someday, of course, maybe on the way back. But it simply doesn't work; the emerald infusion simply doesn't take. Troubleshooting, she discovers the wind inside the tube is indeed magical in nature, but the emerald doesn't care.
When Twilight and Spike arrive at the station, they're equally lethargic. Spike slept from departure to arrival, and is groggy; Twilight, having managed to eke out room to pace in the tiny carriage (she had to traverse it diagonally), is having trouble stomaching the thought of taking another step through this day. But they manage to lug their two suitcases off the chariot and start pulling them towards Golden Oak Library, along Ponyville mainstreet.
There are technicolor ponies loitering anywhere Twilight's eye picks out. Walking along the road, lounging outside cafes, swimming in the lakes. Two unicorn colts are even trying to climb a tree, without much success. Ponyville is so small that it almost seems like the whole town is out enjoying the summer air, but every store she passes has at least one pony in it, too. She feels like every pair of eyes is on her, but she convinces herself she's wrong: Ponyville doesn't typically get many visitors, but plenty of out-of-towners coming in for the Summer Sun Celebration would be arriving today, spending the night, and waking up before sunrise to attend. She probably doesn't stand out at all. Spike might not be so innocuous, but Twilight shouldn't have to deal with anypony before reaching—
Her path is intercepted by a bouncing earth pony, the most vivid pink Twilight's ever seen. Her mane and tail are so fluffy as to make her look like a walking mound of cotton candy. She bounds up close enough for Twilight to see her pastel blue eyes, lets out a deafening gasp truly impressive for her size, and flees as fast as her fuchsia legs can carry her. The whole exchange takes about five seconds, but that's long enough for Twilight to instinctively cower to the ground and start rocking. She stops herself after another second or two, but she knows it's too late; everypony saw, she knows it. Soon, she too is running. She reaches the library, drops her suitcase inside the door, and doesn't cry.