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This 1901 illustrated article from Pearson's Magazine describes an unstoppable technique for defending yourself with a cane or umbrella.
Link (Thanks, Jordie!)You should aim a vicious blow at your assailant's head, holding your hand very high in order to force him to guard high. Simultaneously, you should jump forward from the attacking position, shown in the second photograph, to the position shown in the third photograph, and strike him with the open hand high up on the chest, pulling his foot away from beneath him at the same time -- in order to disturb his balance, and destroy his power to hit you. You could now strike your adversary such a blow with your fist on the face as to render him unconscious, or, of course, you could belabor him with your stick if it were suitable for the purpose.
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.