Galileo Galilei is considered to be the father of modern experimental science. His most significant experiments concerned gravitation. Galileo conducted a series of experiments to measure the effects of gravity on motion, such as measuring the speed of balls of different weights rolling down inclined planes. He found that all objects accelerate at the same, constant rate. He is also famous for the probably apocryphal experiment in which he dropped balls of different masses from the Tower of Pisa. Had the experiment actually taken place, air resistance might have caused the balls to fall at different rates, defying the principle of acceleration that Galileo was trying to demonstrate. In 1609, having heard of the invention of the spyglass, a tube with a piece of glass at each end that made objects appear closer and larger, Galileo set about making his own. Using his telescope, he observed mountains on the Moon's surface (which was thought to be flat), Jupiter's four largest moons, and sunspots. Because he openly supported Copernicus's theory that Earth and all the planets orbit the Sun, Galileo was called before authorities of the Catholic Church and forced to declare the theory false. He was put under house arrest on his own farm, where he continued his scientific work until the end of his life.
An Italian scientist of the late sixteenth and early seventeenth centuries; his full name was Galileo Galilei. Galileo proved that objects with different masses fall at the same velocity. One of the first persons to use a telescope to examine objects in the sky, he saw the moons of Jupiter, the mountains on the moon, and sunspots.