which author was a huge sensation when he/she appeared in a series of
public appearances across the US?

KM --

One guy (with two names) from the day before electronic media -- Mark
Twain, whose real name was Samuel Clemens.  His books were well-known
but his speaking tours in the U.S. and abroad were a sensation:
BoondocksNet
"Mark Twain"
http://www.boondocksnet.com/twaintexts/speeches/

Google search strategy:
"Mark Twain" + speeches

Best regards,

Omnivorous-GA

There are probaby many authors that would fit the (somewhat
inspecific) question that you asked. My first answer would have been
Oscar Wilde, who went on a famous lecture tour around the US in 1882.
It was controversial (because he was always controversial, even before
being brought to court and eventually imprisoned for indecency), but
the tour a huge sensation nonetheless -- the American papers were all
writing about it and he charmed everyone from New Yorkers to Western
miners. (His most famous remark on the tour was when he supposedly
said at the NYC customs house, "I have nothing to declare but my
genius.")

Charles Dickens had also gone on a well-known lecture tour before
Wilde. I believe that the Dickens tour may have been the first
well-known lecture tour by an author in the States, at least by a
non-American author. Hope this helps. There were probably others as
well. If you provide more information, people may be able to provide a
more definite response.