If you’d like to buy a copy of Newton’s Opticks: or, A Treatise of the Reflexions, Refractions, Inflexions and Colours of Light, published in 1704, there’s one on AbeBooks for £131,245.03, plus £12 P&P. Do people just click on such items, I wonder, and wait for the book to plop through the letterbox a few days later?

Anyway, there is a meaning of optics now being heavily used that Newton wouldn’t have understood.