The telescope was one of the scientific revolutions of the seventeenth century. It was unveiled in the Netherlands in 1608; it consisted of a convex and concave lens in a tube, and the combination magnified three or four times. The news of this new invention spread rapidly through Europe, and then Galileo constructed his first three-powered spyglass in 1609. A typical Galilean telescope with which Jupiter's moons could be observed was configured as plano-convex objective with a focal length of about 30-40 inches and a plano-concave ocular with a focal length of about 2 inches. Beginning in the 1640s, the length of telescopes began to increase. From the typical Galilean telescope of 5 or 6 feet in length, astronomical telescopes rose to lengths of 15 or 20 feet by the middle of the century. A 23 feet long telescope was made by Christiaan Huygens, in 1656. It magnified about 100 times, and its field of view was 17 arc-minutes. 
By the early 1670s, Johannes Hevelius had built a 140-foot telescope but it was useless for observation. In 1672, 
Isaac Newton cast a two-inch mirror blank of speculum metal and ground it into spherical curvature and a secondary mirror which reflected the image into a convex ocular lens outside the tube; then he sent this little instrument to the Royal Society, where it caused a sensation; it was the first working reflecting telescope but the effort ended there.
