If the lines you are referring to are:
Imagination! who can sing thy force?
Or who describe the swiftness of thy course?
Then the answer would be 'iambic pentameter'. Because iamb means that there is a sequence of first unstressed syllables, followed by stressed ones, like in this example. Pentameter means there are 10 syllables in one line, because 1 meter = 2 syllables, and penta means 5 meters = 10 syllables.