Necessity is the Mother of Invention
Galileo Galilei moved on to the University of Padua. By 1593, he was desperate in need of additional cash. His father had died, so Galileo was the head of his family, and personally responsible for his family. Debts were pressing down on him, most notably, the dowry for one of his sisters, which was paid in installments over decades (a dowry could be thousands of crowns, and Galileos annual salary was 180 crowns). Debtors prison was a real threat if Galileo returned to Florence.What Galileo needed was to come up with some sort of device that could make him a tidy profit. A rudimentary thermometer (which, for the first time, allowed temperature variations to be measured) and an ingenious device to raise water from aquifers found no market. He found greater success in 1596 with a military compass that could be used to accurately aim cannonballs. A modified civilian version that could be used for land surveying came out in 1597, and ended up earning a fair amount of money for Galileo. It helped his profit margin that 1) the instruments were sold for three times the cost of manufacture, 2) he also offered classes on how to use the instrument, and 3) the actual toolmaker was paid dirtpoor wages.
A good thing. Galileo needed the money to support his siblings, his mistress (a 21 year old with a reputation as a woman of easy habits), and his three children (two daughters and a boy). By 1602, Galileos name was famous enough to help bring in students to the University, where Galileo was busily experimenting with magnets.In Venice on a holiday in 1609, Galileo Galilei heard rumors that a Dutch spectaclemaker had invented a device that made distant objects seem near at hand (at first called the spyglass and later renamed the telescope). A patent had been requested, but not yet granted, and the methods were being kept secret, since it was obviously of tremendous military value for Holland.