 Galileo, then a promising, but unemployed 26-year-old, had written an essay on hydrostatic balance, which struck Guidobaldo as being nothing short of genius.He then commended Galileo to his brother, the Cardinal Del Monte, who referred him to the powerful Duke of Tuscany, Ferdinando I de' Medici.Under his patronage, Galileo got an indication to a professorship of mathematics at the University of Pisa, in 1589.