So, American things of interest to me that happened on February 18th.
1885: The publication of Adventures of Huckleberry Finn in America for the first time, having being published the previous year in the UK and Canada.
1930: Pluto is discovered, from observations made in Arizona.
Today: It's the third monday in February, so - unofficially - it's Presidents' Day. More officially, it's the official (though not technical) Washington's Birthday. It's a bit of a mess in terms of who celebrates what in the USA.