I had a Space Fidgit in the early 1970s (1973 or 1974) when I lived in Illinois. It was a thin disc with weird goo inside that was affected by the heat and pressure of your finger. You could make interesting patterns by rubbing or smearing your finger on the back of it. If it was sold today, they'd call it a stress relieving fidget or an anti-anxiety toy. You might want to check out a semi-similar stress relief toy called the Wham-O Magic Window.

The image below is courtesy of timewarptoys.com:

Below are a couple of pages that have more information and images:

https://clickamericana.com/toys-and-games/space-fidgit-the-magic-color-disc

http://limegong.com/space-fidgit/

Tip Jar