Karl Popper - "Science: Conjectures and Refutations"
I was kindly sent a PDF version of this essay (same as this one). The text is all there, I think, but the textformat is annoying to read. So, I made my own version. The essay itself is about 14100 words long. It is part of the book with the very similar name Conjuctures and Refutations, see Wiki about the book.