Telescopes of Galileo and Newton, 17th century.
© Science Museum / Science & Society Picture Library
These replicas, made in 1923 and 1924, are of telescopes invented by Galileo in c 1609 and Sir Isaac Newton in 1668. Galileo's telescope (right) uses lenses to magnify about 21 times but gives very restricted views so that he was able to see only about a third of the Moon at once. Newton's telescope (left) uses a concave mirror to gather light instead of a simple lens which produces false colour due to the dispersion of light. To use the telescope, the viewer looks through an eyepiece on the side of the tube. The light path is reflected off both the primary mirror and a flat secondary one near the top of the entrance to the tube.