An Italian scientist noted for his experiments and studies on gases, dynamics, and temperature measurement. He studied medicine at the University of Pisa aged 17. At the cathedral in Pisa, he timed the swinging lamp with his pulse and found that the oscillations took equal times. This discovery led to the development of the pendulum clock. He became professor of mathematics at Padua and studied dynamics. It is said that he demonstrated from the Leaning Tower of Pisa that bodies of different weights fell with the same acceleration and also that the path of a projectile is a parabola. He also showed that air has weight by weighing a vessel under ordinary conditions and then filling it by means of a pump with compressed air. He carried out experiments on inclined planes to test his theory of falling bodies. He also made the first thermoscope or temperature detector based on the expansion of air with rise in temperature. He was one of the first scientists to make a practical telescope and discovered the four largest moons of Jupiter in 1610, which are known as the Galilean moons. The Galilean telescope has a convex lens for objective and a concave lens for eye-lens and gives an upright image. His hand-made instruments were in demand all over Europe. He was later persecuted by the Church for supporting Copernicus’ theory that the sun is the centre of the solar system.