The Island of California
Apparently, early Spanish cartographers believed that California was an island separated by the Gulf of California. It was still believed to be an island and was drawn that way on maps despite the fact that explorers actually disproved it with their own eyes. It even took on mythical status as a paradise. I personally do not subscribe to this theory…I think California is a completely different planet.
The Heliocentric Universe
I know I said that I wouldn't discuss geocentrism here, but I will talk about heliocentrism. After the former was disproven by Copernicus, he came up with the latter. Of course, the sun was still the center of the universe, which meant the earth was not too far away. The theory didn't really take off until Galileo had something to say about because he probably had more Twitter followers. Today we realize that there is no center of the universe.
Luminiferous Aether Theory
The earth is moving through goo or some shit. I have no idea what the hell anyone is talking about here. Thank the gods that a couple smart guys from Western Reserve University in Cleveland, OH would fail to detect it, and Einstein didn't listen to any of this and disproved it straightaway.
Apparently, people 500 years ago or so believed that things that burned had a substance in them that caused them to burn (also known as the fifth element [not that weird ass Bruce Willis movie]). From Wikipedia:
"Phlogiston theory states that phlogisticated substances are substances that contain phlogiston and dephlogisticate when burned. Dephlogisticating is when the substance simply releases the phlogiston inside of it and that phlogiston is absorbed by the air.
Growing plants then absorb this phlogiston, which is why air does not spontaneously combust and also why plant matter burns as well as it does."
My new favorite word is Dephlogisticating. Luckily, we now know about oxidation.
The Four Humors
Black Bile, Yellow Bile, Blood, and Phlegm (appetizing, no?) were at one time believed to be the four bodily fluids that must be balanced to maintain health. Today, we have science-based medicine which disproves all of this. Of course, like other theories that have been disproven, there are people out there who can't let go and still believe this bunk.
Oh thank the gods that this is not a thing. Yes, people believed that cavities and other mouth diseases were caused by "tooth worms". Today, we know these things are caused by not brushing, flossing, and going regularly to the dentist (not a humoralist). AUTHOR'S NOTE: Do not click on Image Search after entering the words "tooth worm" into Google.