Winter has already done its worst before the poem begins, and the first stanza shows it with a neat stutter: the forest's ghylls, the steep wooded ravines, are "already blackened / By Winter, are blackened anew." Darkness is laid over darkness. Above them hangs the new moon, compared to "an ivory bugle". The comparison is odd and memorable. The crescent has a bugle's curve and a bugle's pale gleam, but it is silent, a call nobody hears. Sound is planted in the poem before any real sound arrives, and what follows is a slow shift from loud, hostile noise to one small, quiet note.
The noise comes first. The brooks "cut up and increase the forest", a paradox that makes the water both a blade and a multiplier, slicing the woodland into more woodland. They are "roaring with black hollow voices", and the phrase fuses colour and sound so that the gloom becomes audible. The stream cannot settle on an emotion either, caught "Betwixt rage and a moan". Black is the poem's dominant colour so far, and it keeps returning: "blackened", "black", and then, unexpectedly, the charcoal-burners.
The third stanza turns on "But still". The caravan-hut "like a kingfisher gleams between", a flash of bright colour that human life makes against the dark trees. Even the primroses are shy: they "ask to be seen", as though flowers could be tentative. That modesty matters, because the poem keeps preferring small, humble signs of life to grand ones. The charcoal-burners, whose trade is soot, are "black", yet their "linen / Blows white on the line". The washing is the poem's quietest act of defiance, ordinary cleanliness set against the surrounding gloom. The same white appears in "the letter the girl is reading / Under that crescent fine", where the moon returns to frame her. We never learn what the letter says.
That withholding is the poem's central method. The final stanza gives us the girl's brother, "hides apart in a thicket", playing "an olden nursery melody" on a whistle. We are not told the tune or why he hides. The poem suggests tenderness and perhaps shyness, since a nursery song is the music of early childhood, played "slowly and surely" by someone who stays out of sight. Then comes the closing line, "Says far more than I am saying." It is the only place where the speaker steps forward as "I", and he does so to admit that his own words fall short. The boy's music, and by extension the letter and the primroses, carries feeling that description cannot.
The form supports this. Each quatrain pairs two long lines with two shorter ones, and only the second and fourth lines rhyme (blue/anew, known/moan, between/seen, line/fine, playing/saying). The long lines often have a rolling, triple-beat lilt, as in "The charcoal-burners are black, but their linen", which makes the poem sound a little like a tune itself, close to a folk song or a nursery rhyme. The short lines then close each stanza with a quick, plain step. The unrhymed first and third lines leave a small sense of something unanswered, which suits a poem about what goes unsaid. The rhymes are sometimes slightly old-fashioned. "Betwixt" and the inverted "crescent fine" belong to a more ornamental style than ordinary speech, and that decorative diction makes the simple final image stand out all the more.
The title adds one more twist. The instrument is a penny whistle, the cheapest of instruments, yet it appears only in the title; in the poem it is just "a whistle". Against the roaring brooks and the bugle in the sky, it is a tiny sound. The poem's achievement is to let that tiny sound outweigh everything else. Its warmth comes from restraint: a bright hut, some primroses, clean washing, a letter, a tune. These small things hold their ground against a winter that has blackened everything twice over.