This poem alternates between two different types of meter. It has an alternating Iambic Tetrameter and Iambic Trimeter with Catalexis in which the odd-numbered lines (1, 3, 5, etc.) are all in iambic tetrameter. That means there are four ("tetra") iambs per line. The even-numbered lines (2, 4, 6, etc.) are all in iambic trimeter with catalexis. That means there are three ("tri") iambs plus one extra syllable. There are variations on these meters. Not all the lines fit perfectly. For example, the first foot (i.e., beat) of the first line is not an iamb (da-DUM) but rather a trochee (DUM-da, a reverse iamb), and the rest of the line consists of three iambs.