Satire, Written in Heroic Couplets
The form of this poem, as we've already mentioned, is indicated in its title. It's a satire. A satirical poem is one that makes fun of someone or something, and does so in a way that reveals their flaws.
Johnson's poem is a satire because it's a critical poem. It's poem that shows up all the flaws of humankind. We're far from perfect, according to this poem, and in great detail Johnson shows us exactly how, and why, we're not perfect.
In terms of meter, the poem is written in a pattern of heroic couplets. A heroic couplet is made up of two lines of rhymed iambic pentameter. We know we're throwing a lot of terminology at you, Shmoopers, but it's not that complicated. Iambic pentameter just means that you have a line with five (penta- means five) iambs, which are two-syllable pairs in which the first syllable is unstressed, but the second one is stresses (daDUM). But don't take our word for it. Let's take the first two lines of the poem as an example of a heroic couplet:
Let observation with extensive view,
Survey mankind from China to Peru.
You should hear the five iambs at work in these lines: daDUM, daDUM, daDUM, daDUM, daDUM. The alternating stress of the syllables and the rhyme scheme of these two lines indicates that they're a heroic couplet.
In English poetry, heroic couplets were popularized by Alexander Pope. Pope was Johnson's predecessor and an important influence on Johnson's own work. Both our title (where he name drops Juvenal) and the form and meter of this poem show us that Johnson was working in the solidly classical tradition. He's old school all the way here.