Of circadian rhythm: https://www.nationalgallery.org.uk/paintings/vincent-van-gogh-a-wheatfield-with-cypresses https://en.wikipedia.org/wiki/Wheat_Field_with_Cypresses https://iwp.uiowa.edu/whitmanweb/en/writings/song-of-myself/section-21 https://whitmanarchive.org/archive1/classroom/student_projects/brian/pagetwo.html https://whitmanarchive.org/published/LG/1871/poems/15 https://www.vincentvangogh.org/starry-night.jsp (the above reference contains no mention of the poetic Whitman connection!)