 After leaving university, Galileo worked as a private mathematics tutor around Florence and Siena and cultivated the support of leading mathematicians. He visited Christoph Clavius, professor at the Jesuit Collegio Romano, and corresponded with the engineer Guildobaldo del Monte, Marchese of Urbino. In 1588, he applied and was turned down for a professorship in Bologna, but a year later, with the help of Clavius and del Monte, he was appointed lecturer in mathematics at Pisa. In 1592, he obtained, at a much higher salary, a chair of mathematics at the University of Padua, in the Venetian Republic. Galileo also supplemented his income by producing a calculating instrument of his own design (see Galilei 1606) and other devices in a household workshop, and by private tutoring and consulting on practical mathematics and engineering. During this period, he began a relationship with Marina Gamba, and their daughter Virginia was born in 1600. In 1601, they had another daughter, Livia, and a son, Vincenzo, in 1606.