I Kept on the Field".
This writer described a "look I shall never forget" from the face of a deceased son and comrade in   "Vigil Strange I Kept on the Field". The narrator of one of his short poems tells of becoming "tired  and sick" before leaving a lecture; that poem is "When I Heard the Learned Astronomer". One of his   long poems states "What I assume you shall assume" and "I am large, I contain multitudes." This  poet wrote "Our fearful trip is done" in one of his works remembering Abraham Lincoln, entitled "O  Captain! My Captain!". Name this poet of "Song of Myself", whose works were collected in Leaves of  Grass.
This writer described a "look I shall never forget" from the face of a deceased son and comrade in  
Walt(er) Whitman