Problem is that's not a source. There are plenty of famous misquotes that get bandied around, yet when we look for the actual origin, we're left empty-handed, e.g. "640k ought to be enough for anyone", "let them eat cake" etc.
Just Google it. The link i posted is from a well-respected science and technology magazine.
What is surprising is that there were birds flying in 1895 (and much earlier). It does seem strange that Lord Kelvin stated the above quote. But I also doubt that New Scientist would misquote Lord Kelvin...
Another related link, from Wolfram Research (another well-respected source).