Galileo’s Telescopes: Seeing is Believing
Few events in history have proved as momentous as Galileo’s discovery of the moons of Jupiter. But would sharing his findings mean sharing his telescope?
Four hundred years ago, Galileo Galilei (1564-1642) was in a state of anxiety. In January, he had discovered four moons orbiting Jupiter. In March, he had published this and other remarkable discoveries made with his improved telescope in Sidereus Nuncius (‘The Starry Messenger’). But by the summer, he was becoming profoundly alarmed. He had offered philosophers and mathematicians in Venice, Padua, Florence, Pisa and Bologna the chance to look through his telescope and confirm his discoveries. Some, including Cremonini, the highest-paid academic in Italy and a good friend of Galileo’s, had simply refused. Others had looked, but had said they could not see what on earth he was talking about. Only Kepler in Germany had come out in his support, but he had yet to get hold of a decent telescope, so had not seen the moons for himself. He was prepared to believe Galileo because he – and hardly anyone else – shared Galileo’s Copernicanism.
Galileo had to wait patiently that summer as Jupiter had disappeared from the night sky. He was also in something of a quandary; if he gave good telescopes to other astronomers, then they might make new discoveries with his equipment (Galileo’s most important telescopic discovery, the phases of Venus, which more or less destroyed Ptolemaic astronomy, was to come within a few months, in December 1610). Worse, if he gave them telescopes and they were unable to make sense of what they saw, his reputation might be permanently damaged.
What he wanted was for them to make their own telescopes. In the autumn, this began to happen – Thomas Harriot in England and Nicolas-Claude Fabri de Peiresc in France saw the moons for themselves, but no one told Galileo. Kepler got hold of a Galilean telescope and confirmed Galileo’s discoveries. Above all, in Rome, the Jesuit mathematicians finally announced in December that they had confirmed all of Galileo’s discoveries. By the spring of 161,1 the moons of Jupiter had become an established fact.
These months, from March to December 1610, saw the birth of modern science. Before 1610, no one had ever thought that the task of scientists was to make discoveries. As Galileo complained in a letter to Kepler in August, philosophers assumed that sound knowledge came from comparing texts, not developing new instruments (Cremonini went on to write a long book on the heavens, promptly banned by the Catholic Church, in which the telescope and Galileo’s discoveries are never mentioned). It is safe to say that prior to 161,0 not a single significant scientific argument had turned on a question of fact. Now, Galileo began to be compared by his contemporaries with Vespucci, Columbus and Magellan, the discoverers of new lands.
During the last 400 years, science has transformed our world as discovery has succeeded discovery. Telescopes and microscopes, steam engines and internal combustion engines, electricity and nuclear power, antiseptics and antibiotics. Galileo had no idea what the future would bring, but he did have a clear idea that the job of a scientist was first to establish the facts (he says so in a letter of 1615 to Christina of Lorraine, Grand Duchess of Tuscany, the mother of Cosimo II de’ Medici). In relying on the idea of fact, Galileo was using a new language. Previously, scientists had discussed the phenomena, but Aristotle had been clear that any generally established belief counted as a phenomenon to be explained; he and his successors had no clear notion of establishing the facts by testing beliefs and seeing if they were well-founded or not, just as they had no term for a ‘fact’. Thus, for thousands of years, no one doubted Aristotle’s claim that the speed at which objects fall is proportional to their weight. What worried them was how to define light and heavy, lighter and heavier. By 1610, Galileo had carried out meticulous experiments on falling bodies, but he hadn’t published the findings. It was the telescope that brought to public attention the idea of a new science, founded on new facts.
In 1616, Copernicanism was condemned by the Catholic Church, and in 1633, Galileo was tried and condemned by the Inquisition for arguing in favour of it. For centuries, the trial of Galileo has received far more attention than any other aspect of his life. The conflict between religion and science still rumbles on in the debates over Darwinism and intelligent design. These arguments matter to us, but the trial of Galileo provoked little debate at the time and news of it spread slowly. In 1633, few were prepared to dispute the competence of theologians and philosophers to pass decrees on scientific questions. Indeed, the idea of ‘science’ as separate from philosophy was precisely what was at stake in the years after 1610. Now, when we hold enquiries into whether climate scientists have manipulated their statistics, or wait to hear if some new drug survives a controlled trial, we take scientific authority and objectivity for granted. Harriot, the English mathematician, made almost all of Galileo’s discoveries independently, but he never published the results, and so they were never open to wider examination. Galileo in 1610 invited the world to look through his telescope, and at that moment, the idea of progress (up to then a concept peculiar to artists, mathematicians and anatomists) came of age. We still live in the world first inhabited by the readers of Sidereus Nuncius.