Set of four small phials ending in a bulb. The phials contain acquarzente, in which small glass spheres of different density are immersed. The rise in temperature causes an increase in the volume of the acquarzente, reflected in the movement of the small spheres (first the less dense, then the more dense). Because of the spheres' sluggish motion, this thermometer was also called infingardo [slothful, slow]. The invention of this model is attributed to Grand Duke Ferdinand II de' Medici.