Late 1800s

X-rays were all the rage, rightly so, because X-rays are awesome.

Everyone was going bananas for trying to understand them, see if there were other kinds of invisible

rays that you see bones and other cool stuff. And so there's this whole cottage industry

of making x-ray machines and learning about x-rays and playing with them. And then meanwhile,

in parallel to that, scientists began to

get interested in phosphorescent materials. These are materials or elements that glow in the dark

after being exposed to light, especially x-rays. If you shine a bunch of x-rays on a phosphorescent

material, and then you wait for it to get dark,

the material will glow. Now, these kinds of things have been known for literally forever,

but now scientists were starting to pay more attention to it after all. Interesting glowing

objects, x-rays, really loving this stuff. This is good, juicy science right here.

And French scientist Henri Beccarell was monkeying around with different phosphorescent materials.

He was taking pictures of them. He was smelling them. He was talking to them.

You know, the works. And at some point, in his investigation

of various phosphorescent materials and minerals and rocks and whatnot, he put a piece of paper

over a photographic plate and then put the phosphorescent material on top of the paper to see

if he could still take a picture of it.

Now, why did he do this? Well, remember, everyone was super fascinated by invisible rays. No one

could see x-rays, but they would show up on a photographic plate. And everyone was interested

in phosphorus materials, and they thought there was some sort of interesting connection between

the two. And that if there are x-rays, maybe there are other kinds of rays.

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