A frozen street, a rush of boys on sleds, and then, almost before we have registered them, they are gone. Dickinson's eight lines hold a small drama of loss inside a winter scene, and the surprise is where the weight lands. It falls not on the sleds but on the flat, ordinary present left behind them.
The first stanza sets the scene in glitter. "Glass was the Street" is a metaphor with no "like" or "as" to soften it: the ice does not resemble glass, it simply is glass, smooth, shining and breakable. The next phrase is odder. "Tinsel Peril" dresses danger in the cheap sparkle of decoration, so that beauty and risk become one surface. Then comes "Tree and Traveller stood." Pairing a tree with a person makes the human figure as motionless as the plant, and the verb "stood" suggests a hush, perhaps a cautious pause on the slippery ground, though the poem never says why. Against that stillness the rest of the stanza bustles. The air is "Filled" with "merry venture," and the road is "Hearty with Boys," as though the boys were a quality of the road itself, the way heartiness belongs to a meal.
In the second stanza the energy turns to speed. "Shot the lithe Sleds" puts the verb first, so the sentence launches the way the sleds do. "Lithe" makes them sound like supple animals, and "shod" hints at metal-fitted runners. The strangest word is "vibrations." The sleds stop being objects and become something heard and felt, a tremor in the air. Then comes "Emphasized and gone," where two words hold both the arrival and the disappearance. "Emphasized" does quiet work here, because it prepares the metaphor the poem ends on.
That ending is the poem's real subject. "It is the Past's supreme italic / Makes this Present mean." Italic type slants a word to make it stand out from the line around it. The idea seems to be that vanished moments are the ones memory stresses most strongly, set apart from the plain print of everyday life. The word "mean" can be read in two ways. It can be a verb, so that the past's emphasis gives the present its meaning. It can also be an adjective, so that the past makes the present seem shabby and small. Dickinson drops the word "that" that would normally link the clauses, which packs the grammar tight enough to hold both readings. Judging by the poem's tone, the second reading is the sharper one, but the first keeps it from being simple regret.
The sound of the poem works against neatness in a similar way. Lines alternate between longer and shorter, roughly like a loosened hymn stanza, and the rhymes are slant: "stood" and "Road," "gone" and "mean." Each pair almost matches, and the near-miss leaves a faint feeling of something unresolved. The first and third lines of each stanza ("Peril" and "venture," "vibrations" and "italic") find no real partner at all. The poem also ends on a dash rather than a full stop, so it breaks off in mid-thought, just as the sleds vanish mid-motion. Her habitual capitals on words like Street, Air, Past and Present make them sound almost like characters. The Past and the Present become two rivals, one grand and emphasized, the other left standing in the cold.
The poem is worth reading for how it moves from a visual scene to an idea, in only the last two lines. For six lines we are simply watching: ice, boys, sleds. Then one typographic term turns the scene into a claim about how memory works, which is that we value a moment most sharply once it has slipped out of reach. It is also a nice irony that Dickinson, whose poems mostly stayed out of print during her lifetime, reaches for a printer's word to explain it. The metaphor is exact, compressed and a little startling, and it makes a speeding sled feel like a lesson in loss.