Why does the composer use the french horn in the nocturne of a midsummer's night dream?

Answer 1

I can only assume the composer wished to use the soft, gentle timbre of the Horns for this most peaceful of excerpts. Any other instrument may have been too harsh or not blended well with the attempts of subtle orchestration. Only a gander.

Answer 2

The composer likely chose the French horn for its rich, warm tone that can evoke a sense of mystery and magic, which are often associated with nocturnal settings and Fairy Tales. The French horn's sound can add depth and color to the music, enhancing the dreamlike quality of the piece.