Long measure is simply four lines of iambic tetrameter rhyming abab. The term "measure" connects it with hymnology; in hymnals the abbreviation "LM" that appears in connection with hymn titles identifies their meter or measure; there it sometimes is thought of as denoting four lines of eight syllables. To some extent long measure may be the inheritance of an effort to write iambic octameters, lines that are really too long for Enlgish poetry and which tend to split in half.

                            O wish that's vainer than the plash
                             Of these wave-whimsies on the shore:
                            "Give us a pearl to fill the gash --
                             God, let our dead friend live once more!"

                            O wish that's stronger than the stroke
                             Of yelling wave and snapping levin;
                            "God, lift us o'er the Last Day's smoke,
                             All white, to Thee and her in Heaven!"

                            O wish that's swifter than the race
                             Of wave and wind in sea and sky;
                            Let's take the grave-cloth from her face
                             And fall in the grave, and kiss, and die!

                            Look!  High above a glittering calm
                             Of sea and sky and kingly sun,
                            She shines and smiles, and waves a palm --
                             And now we wish -- Thy will be done!
                                                               --Sidney and Clifford Lanier

                            Oh! did those eyes, instead of fire,
                                With bright, but mild affection shine:
                            Though they might kindle less desire,
                                Love, more than mortal, would be thine.

                            For thou art form'd so heavenly fair,
                                Howe'er those orbs may wildly beam,
                            We must admire, but still despair;
                                That fatal glance forbids esteem.
                                                                                --Byron