Tell the temperature on this glass thermometer by reading the tag of the lowest floating sphere in the upper part of the cylinder. Modeled on the thermoscope invented by Galileo Galilei in the 1600s, it relies on the downward pull of gravity (acting on the counterweighted tags) and the upward pull of buoyancy (acting on the colorful liquid inside the glass bubbles). As the air temperature changes, so does the density of the liquid surrounding the bubbles. Each bubble reacts by rising or sinking, coming to rest in a position where its density is equal to the surrounding liquid. The sealed glass cylinder includes 7 spheres; it registers approximate temperatures between 62°F and 86°F. 15" high. Ages 6 and up.