This attractive 17" thermometer contains 7 floating spheres and is based on Galileoï¿½s discovery that a liquidï¿½s density decreases as its temperature increases. This unique device consists of a sealed glass cylinder containing multi colored floating spheres. The spheres have different weights that rise and fall at different temperatures. Current temperature is indicated by the tag attached to the lowest of the floating spheres. Use in science classes to demonstrate Galileoï¿½s principle or as an interesting and attractive way to accurately measure indoor ambient temperature anywhere. Contains 7 floating sheres, measuring from 72 degrees F to 84 degrees F in 2 degree increments.