In the first known article signed " Yours, dreamily, Mark Twain," reference 
 is made by Twain of his playing the piano. He wrote:  "I sat down  to the 
piano and sang - however, what I sang is of no consequence to anybody. It  
was only a graceful little gem from the horse opera. "
 
A dictionary today says Horse Opera is "A film or other theatrical  work 
about the American West; a western"
 
The first written "westerns," often later called "Dime Novels" or "Dime  
Westerns" made their appearance in about 1860. But of course, no western  
movies until a long time after that. So what was the music Twain was  playing on 
the ivory keys at former California governor J. Neely Johnson's party  in 
Carson City? 
 
The Sheboygan Journal of May 21, 1857, page one, col. three  says ". . . to 
the circus, more tastefully termed the 'horse opera,' which last  is 
patronized to a greater extent in this city than any other place of  amusement." I 
found a few other newspaper references confirming it as  a mid-1800s term 
for a Circus.
 
Twain, taught piano by his sister, was tinkling out a piece  of circus 
music of the period.
 
Bob Stewart