|Radiation dose monitor.
This isn't exactly a spinthariscope, but the principle is similar so I'm listing it in the spinthariscope category. (Spinthariscopes are explained in more detail here.)
This is actually a dose rate monitor that works as follows. At one end is an eye piece with a lens that focuses on a split screen inside the device. Half of the screen is illuminated by a small light bulb, with the brightness controlled by a dial on the back end. The other half is a phosphorescent screen that glows when exposed to radioactivity. To measure the current radiation level you look into the eye piece and adjust the dial until the two halves of the screen appear to have the same brightness. Then you can read the radiation level off the markings around the dial on the back.
Or you could just run like hell if you see any glow at all. The dose rates necessary to register visibly on the phosphorescent screen are high enough that you really wouldn't want to hang around in an area where this monitor would register a visible dose.
Source: eBay seller geoelectronics
Contributor: Theodore Gray
Acquired: 19 May, 2007
Text Updated: 19 May, 2007
Sample Group: Spinthariscopes