Four-line stanzas with lines 1,2, and 4 in iambic trimeter and line 3 in iambic tetrameter are a hymn stanza known as common measure. Emily Dickinson's poem is a good example:

                           Then, as horizons step,
                               Or noons report away,
                            Without the formula of sound,
                               It passes, and we stay:

                            A quality of loss
                               Affecting our content,
                            As trade had suddenly encroached
                               Upon a sacrament.