This vintage toy ad — torn from the back pages of a 1942 comic book — invites you science-minded kids to place a miniature telescope to your eye, which just happens to contain "a small quantity of real radium."
Another winning quote from the ad copy: "The RADIUMSCOPE is also a wonderful night-guide. IT GLOWS WITH A WEIRD LIGHT IN A DARK ROOM."
The Radiumscope's the most amazing sight you ever saw! Of course, what you might mistake for "the destruction of thousands of miniature worlds" is, in reality, simply the radioactive cell death of your eyeball's photo receptors, experienced in thrilling first person!
Years later, two Radiumscopes would be pushed through a pince-nez, and the prototypical X-Ray Specs were born, marketed to the man who just can't get it up unless he can see a lady's scapula.
Most Amazing Sight You Ever Saw! [Lileks]
UPDATE: Daniel Rutter edifies us in the comments about the true, scientific nature of the radiumscope...
This is actually a spinthariscope; a speck of radioactive material sits on the other side of a zinc sulfide screen that glows when alpha particles hit it.
So what you see is not some effect of radiation hitting your retina (which actually wouldn't stimulate it at all), but harmless visible-light photons, and not too many of them, either. It has been observed that even though you need completely dark-adapted eyes to see the feeble display from a spinthariscope, it's pretty amazing that you can see anything at all.
Edifying! Thanks, Dan. I'm still not crazy about douching out my eye socket with one, though.