When most liquids are cooled, the particles settle into a regular order, and the liquid becomes a solid. But helium atoms are so light and weakly drawn to one another that even when ordinary atomic motions have quieted, the atoms jiggle with zero-point motion, a slight momentum imparted by the quantum uncertainty principle. Hence, they never settle into the solid state.
The first seismograph was invented in 132 A.D. by the Chinese astronomer and mathematician Chang Heng. It consisted of a ceramic urn with eight dragons attached to its sides. Each dragon held a small bronze ball in its mouth. Whenever there was even a slight earth tremor, a mechanism inside the seismograph would open the mouth of one dragon, and the bronze ball would fall into the open mouth of one of eight toads sitting below. Imperial watchman could tell which direction the earthquake came from by seeing which dragon's mouth was empty.