The book that explained the tides

Newton's Principia was published at Halley's expense, and Book III does something nobody had managed before: it works out the tides from the Moon.

Everyone had known for millennia that the tides follow the Moon. Newton was the first to say why, and to get the awkward part right — that there is a bulge on the far side of the Earth too, so most coasts get two high tides a day rather than one. The Royal Society had spent its money on a book about fish, so Halley paid for this one himself.