The technical term for the rhythm of this poem is "iambic tetrameter," but don't get all freaked out by those strange words. An iamb is a two-syllable combination, where an unstressed syllable is followed by a stressed syllable. Think of the word "alarm," which is pronounced "uh-LARM." And "tetra-" just means four. So, iambic tetrameter just means that the poem has four beats per line (with a few exceptions), and these beats happen to be arranged in a repeating pattern of iambs, four in (almost) every line. Check out an example of the basic structure, then we'll move on to the variations. Stressed syllables are in bold:
The Child is fa ther of the Man;
If you read that line aloud, you should hear the iambic tetrameter pattern: da-DUM da-DUM da-DUM da-DUM. Got it? Great. Now let's complicate things for you.
If you read the whole poem aloud, you should be able to hear those iambic beats fairly clearly, but some irregularities should stand out, too. Two obvious variations on the iambic tetrameter are in lines two and six, which are noticeably shorter than the other lines (and indented, too). They are iambic, with the same stressed pattern, but are in trimeter (line 2) and dimeter (line 6). This means that instead of having four beats, like a line of tetrameter would, they only have three beats for trimeter and two beats for dimeter. Check it out:
A rainbow in the sky:
In this line of iambic trimeter, you should hear three iambs: da-DUM da-DUM da-DUM. When you read line 6 out loud, you get only two: da-DUM da-DUM.
So, why would Wordsworth vary his iambic meter? Was he bad at poetry? Um, no. Was he bored? Probably not. If you think about it, these changes in the established rhythm stand out to us readers. Therefore, they get special emphasis. In line 2, both the visual indentation on the page, as well as the shift in rhythm, make us really pay attention to that rainbow. And the same can be said for the speaker's "let me die!" plea in line 6. We get a stronger sense of the speaker's emphasis from these variations.
Now that you have that under your belt, let's raise the bar even higher, shall we? There's a slightly trickier variation at the very end of the very last line. This is where the rhythm gets a little complicated. You'll notice that the pattern of stressed and unstressed syllables is disturbed by the words "natural piety," which are a little bulky and long to fit into iambic tetrameter. It reads:
So, you should hear DUM-da-da DUM-da-da. When you do, you're hearing two dactyls. No, not pterodactyls, two dactyls. What's a dactyl? Well, it's a group of three syllables where the first one is stressed, followed by two unstressed syllables. Unlike every other line, which ended in a stressed syllable, the last line ends more softly with this pattern. It's as though the speaker is at peace with this mention of natural piety. We're left with a rhythmic sense of calm.
Also notice that this poem has a rhyme scheme: the first and fifth line rhyme, the second and sixth line rhyme, and the third, fourth, and seventh lines rhyme. Then the eighth and ninth lines rhyme. These rhymes follow no rigid pattern, but still the presence of these rhymes ties the poem together in a way that's pleasing to the ear. This varying rhyme seems a pretty appropriate choice for a poem that is describing the joys of the natural world, don't you think? We mean, things in nature can be really pretty, but they're not always symmetrical. Does a rose bush follow a set pattern? Not really. It just blooms willy-nilly, the way these rhymes bloom in the poem.