How did Galileo Galilei support himself financially while teaching at the University of Padua?

While teaching at the University of Padua from 1592 to 1610, Galileo Galilei faced significant financial pressure as the head of his family following his father's death. Although he held a university chair, his salary was insufficient to cover his expenses.1

To supplement his income, Galileo employed several strategies:

• Private Tutoring: He took in well-to-do boarding students and provided them with private instruction in subjects such as fortification.1
• Commercial Inventions: He designed and sold a proportional compass, or sector, which was manufactured by an artisan he employed in his home.1
• Institutional Rewards: In 1609, after presenting an improved telescope to the Venetian Senate, he was granted life tenure and a doubling of his university salary, making him one of the highest-paid professors at the institution.2