6.5 Galileo's telescope  (Page 2/4)

In the literature of white magic, so popular in the sixteenth century, there are several tantalizing references to devicesthat would allow one to see one's enemies or count coins from a great distance. But these allusions were cast in obscurelanguage and were accompanied by fantastic claims; the telescope, when it came, was a very humble and simple device. Itis possible that in the 1570s Leonard and Thomas Digges in England actually made an instrument consisting of a convex lensand a mirror, but if this proves to be the case, it was an experimental setup that was never translated into amass-produced device.

The telescope was unveiled in the Netherlands. In October 1608, the States General (the national government) in The Haguediscussed the patent applications first of Hans Lipperhey of Middelburg, and then of Jacob Metius of Alkmaar, on a device for "seeing farawaythings as though nearby." It consisted of a convex and concave lens in a tube, and the combination magnified three or fourtimes.

The news of this new invention spread rapidly through Europe, and the device itself quickly followed. By April 1609three-powered spyglasses could be bought in spectacle-maker's shops on the Pont Neuf in Paris, and four months later therewere several in Italy. ( ) We know that Thomas Harriot observed the Moon with a six-powered instrument early in August 1609. But it was Galileo who made the instrumentfamous. He constructed his first three-powered spyglass in June or July 1609, presented an eight-powered instrument to theVenetian Senate in August, and turned a twenty-powered instrument to the heavens in October or November. With thisinstrument ( ) he observed the Moon, discovered four satellites of Jupiter , and resolved nebular patches into stars. He published Sidereus Nuncius in March 1610.

Verifying Galileo's discoveries was initially difficult. In the spring of 1610 no one had telescopes of sufficient quality andpower to see the satellites of Jupiter, although many had weaker instruments with which they could see some of the lunar detailGalileo had described in Sidereus Nuncius . Galileo's lead was one of practice, not theory, and it tookabout six months before others could make or obtain instruments good enough to see Jupiter's moons. With the verification of thephases of Venus by others, in the first half of 1611, Galileo's lead in telescope-making had more or less evaporated. The nextdiscovery, that of sunspots , was made by several observers, including Galileo, independently.