In 1591 Vincenzo Galilei, Galileo's father, died and since Galileo was the eldest son he had to provide financial support for the rest of the family and in particular have the necessary financial means to provide dowries for his two younger sisters.
Sa April 1641 Castelli manlalakbay mula sa Roma sa Venice at, sa paraan, tumigil sa Arcetri upang bigyan ng Galileo ang isang kopya ng Torricelli ang sinulat ng kamay at iminumungkahi na siya trabaho sa kanya bilang isang assistant.