Previous natural philosophers mostly read what the ancients had written, thought about it, argued with each other about it, and accepted their conjectures as scientific fact. Many of these supposed truths were trivial to invalidate by actually going out in the world and measuring things, but that didn't come into fashion until relatively recently.
This brief history of science is often taught inside of chemistry classes. My teacher had a great time telling us about the beliefs that preceded our current understanding of the atom and how we came to reject them.
But then you get a bunch of people who said things like "hey, what if I actually throw two different cannonballs off a tower? Does the heavier one get to the bottom first?"
(That particular one can actually be figured out by a thought experiment, so maybe not so great an example.)
People did amazing things like measure the value of G in their basements. Flying kites to see WTF electricity is. Making rainbows with prisms. And it just keeps going...
Armchair scientists like myself like to read about science, but without people actually having a look, we're back in ancient Greece.
Makes you wonder how much we'd have achieved if people had gotten off their asses a bit earlier than a few hundred years ago.