In the mid-1660s he used a glass prism to throw a rainbow-like spectrum on his wall, and pondered on ’the celebrated phaenomena of colours’. Among those who confronted this defect was Isaac Newton. Galileo and his successors produced increasingly powerful instruments, but found that high magnification telescopes suffered from chromatic aberration - blurred images caused by the differing refractivity of differently coloured light. (His interpretation of these observations got him into trouble later, but that’s another story.) In particular, his discovery of satellites orbiting Jupiter revealed another centre of motion in the universe besides our own planet. Several of the observations he described in The starry messenger (1610) challenged astronomical orthodoxy. Before seeing the Dutch devices, he deduced how they must work and constructed one himself. Galileo was professor of mathematics at Padua, Italy, but also a skilled craftsman who made his own instruments. So it was Galileo Galilei who, in December 1609, made the first telescopic discoveries to be communicated to the scientific world. The English mathematician Thomas Hariot turned one on the moon in July 1609, but published no results. Hans Lippershey claimed priority, but while wrangling over patents continued, the instruments were distributed (and copied) across Europe. However, it is certain that by 1608 several Dutch spectacle-makers were selling pairs of lenses in sliding tubes, later known as telescopes. Several 16th century authors, including Giovannibattista della Porta and Thomas Digges published descriptions of far-seeing devices, but as they never demonstrated them publicly we cannot be sure they really existed. They may have been true, for when someone with hyperopia - a form of long-sightedness - looks through a convex lens at a suitable distance it combines with the defective lens in their eye to act as a crude telescope. Rumours abounded about ’magical’ devices enabling people to see distant objects enlarged. Greek, Roman and Arabic scholars had noted the magnifying power of lenses, but it was only in the late 13th century that European artisans started making spectacles to improve defective vision. However, great discoveries seldom emerge from a single Eureka! moment and, while celebrating these anniversaries, we should remember that there were telescopes before Galileo, and spectroscopes before Bunsen and Kirchhoff.
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