There is one comment we do not recommend:
That quote is variously stated to be found in a report to the U.S. Congress or a letter to President McKinley or somesuch but has never been produced in document form.
Here's the patent law blog PatentlyO:
Charles H. Duell was the Commissioner of US patent office in 1899. Mr. Deull's most famous attributed utterance is that "everything that can be invented has been invented." Most patent attorneys have also heard that the quote is apocryphal....
***However, with a bit more searching, I came across an 1899 edition of Punch Magazine that had been donated to Harvard University by the Pulitzer family. In that edition, the comedy magazine offered a look at the "coming century." In colloquy, a genius asked "isn't there a clerk who can examine patents?" A boy replied "Quite unnecessary, Sir. Everything that can be invented has been invented."
I suspect that 1899 joke is the origin of the expression. Of course, there is still Ecclesiastes.