Beaver Brook at Waverley was a favorite resort of Lowell's and it is often mentioned in his writings. In summer and winter it was the frequent goal of his walks. The poem was at first called The Mill. It was first published in the Anti-Slavery Standard, and to the editor, Sidney H. Gay, Lowell wrote:—"Don't you like the poem I sent you last week? I was inclined to think pretty well of it, but I have not seen it in print yet. The little mill stands in a valley between one of the spurs of Wellington Hill and the main summit, just on the edge of Waltham. It is surely one of the loveliest spots in the world. It is one of my lions, and if you will make me a visit this spring, I will take you up to hear it roar, and I will show you 'the oaks'—the largest, I fancy, left in the country."

21. Undine: In mythology and romance, Undine is a water-spirit who is endowed with a soul by her marriage with a mortal. The race is the watercourse conducted, from the dam in an open trough or "penstock" to the wheel.

45. In that new childhood of the Earth: This poem was written a few weeks after the Vision of Sir Launfal was published, and it therefore naturally partakes of its idealism.