Talk about a few coincidental discoveries ~ inventions

Watt didn't invent the steam engine, he improved it. There is another person, Stephen, who is also worth mentioning.

The discovery of iodine is a coincidence. The cat knocked over the bottle of concentrated sulfuric acid in the seaweed ash basin.

And use vaccinia to prevent smallpox. -Jenner (from The Milkman)

Buoyancy measurement, Archimedes bathing.

The invention of the telescope.