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!)