Nothing meets the eye to demonstrate beyond doubt that autumn has come - yet suddenly we are struck just by the sound of the wind (Kokin Wakashu, Aki no Uta Jo (the first volume of Autumn Poems), 169).
秋来ぬと目にはさやかに見えねども風の音にぞおどろかれぬる（古今和歌集、秋歌上、169）