“Continually and Continuously. It seems that these words should have the same meaning, but in their use by good writers there is a difference. What is done continually is not done all the time. But continuous action is without interruption. A loquacious fellow, who nevertheless finds time to eat and sleep, is continually talking; but a great river flows continuously.”
Excerpted from: Bierce, Ambrose. Write it Right: A Little Blacklist of Literary Faults. Mineola, NY: Dover, 2010.