We hear two sounds running through this poem, two rhythms, two tones that intermingle and reinforce each other. We picked musical instruments to capture the spirit of each, but let's see if you can hear what we mean.
Try reading those first four lines of the poem. Can you hear that short, sharp, rat-a-tat sound of the words, like "pipe is lit" (1) or "fire I sit" (3)? Tap-tap-tap. Not one word in the first four lines is longer than a syllable, and most of them have a sharp, tinny sound, like a snare drum. We're talking about happy, light things, and the bright drum sound sets the right mood.
Then, as sadder thoughts creep in, we start to hear a rounder, deeper, smoother sound. That's the cello. It plays the melody of those open, wide "O" sounds that crop up throughout the poem. Say this one out loud: "A moment, and the prompter's chime/ Will ring the curtain down on you" (11-12). Do you hear how slow and wide those sounds are? They're totally different from the opening.
That snare drum sound isn't gone for good, though. It's definitely there at the end: "There! bless you now! Old Year, good-bye!" (56). See? Tap-tap-tap again. In fact, a lot of the tension and emotional power of the poem comes from the struggle between these two feelings (sharp and happy vs. slow and sad) and the sounds that represent them.