Columbia subject headings:
Field, Eugene, 1850-1895.
Twain, Mark, 1835-1910.
Harvard subject headings:
Field, Eugene, 1850-1895.
Twain, Mark, 1835-1910
Princeton subject headings:
Authors, American--19th century--Biography.
Field, Eugene, 1850-1895--Travel--Europe.
Twain, Mark, 1835-1910--Travel--Europe.