Galileo's first signed text, the Operations of the Compass, has been presented as an educational toy to be used for the instruction of Prince Cosimo de' Medici. What it really described, however, was the operation of a highly evolved, precise instrument, designed to find answers, by applying mathematical laws, to the new questions posed by technological progress in the military field and the practical disciplines in general.
Seeking financial gain and instant fame, several people tried to pass off Galileo’s invention as their own. The most sensational case was that of Baldassarre Capra, who published a Latin translation of the Operazioni del compasso geometrico e militare, signing it as if he were the author.
Using the telescope for the first time as a scientific instrument rather than a curious toy, Galileo explored the sky. Before his eyes appeared not only the wonders of nature, but also the physical proof that many of the current astronomical theories, derived from Aristotle, were in reality false.
A group of Florentine Aristotelians led by Lodovico delle Colombe managed to engage Galileo in an argument on floating. According to their descriptive physics, the different behaviour of bodies in water depended on their different shapes. To this concept Galileo opposed Archimedes’ hydrostatic laws, based on differences in specific weight, an idea extraneous to the Aristotelian tradition.
In observing the Sun through the telescope, Galileo had seen numerous spots on its surface. Elsewhere, these same spots had been noted by Christoph Scheiner, a Jesuit mathematician residing at the time in Bavaria. Mark Welser, an eminent citizen of Augusta who was acquainted with both Galileo and Scheiner, asked their opinions on the new discovery.
In ecclesiastical circles Galileo’s explicit advocacy of the Copernican cosmology aroused the fear that error might be demonstrated in the Holy Scriptures, which clearly stated that the Sun moved. Especially among the Dominicans in Florence, alarmed voices were raised, resulting in a denouncement to the Holy Office.
The three comets that appeared between 1618 and 1619 gave rise to another heated argument, this time between Galileo and the Jesuit priest Orazio Grassi.
Although his diplomatic attempts to have the Church recognize the heliocentric system and the motion of the Earth had failed, Galileo held firm to his long-time intention of writing a cosmological work. For years he had attentively observed the tides in the sea. He now believed he had found in them physical proof of the Earth’s combined diurnal motion and annual motion.
After his trial and condemnation, Galileo was prohibited by the Inquisition from studying cosmological issues or publishing any of his writings. But his incessant curiosity would not let him abandon his studies, although now focussed on terrestrial, rather than celestial physics.