One question to ask. "Who was there when Galileo stood on the tower?" A good answer says: we only have his pupil's word, and the pupil was not born yet.

One thing to do at the table. Drop two things of different weight from the same height, a spoon and a grape, onto a tray. Listen for one sound or two. Then ask: does this tell us anything about what Galileo did? (It tells us how things fall. It cannot tell us who stood on a tower.)

Make a two-column page. On the left, in ink, write a family story you have a source for: a letter, a photo, a person who was there. On the right, in pencil, write the version people like to tell. Which side is longer?

The grown-up layer. Beto's test is good science and the wrong tool for history. A true idea is not a true event. The only account of the tower drop is Vincenzo Viviani's life of Galileo, composed in 1654 and printed in 1717; Galileo himself never describes it. Simon Stevin, by contrast, dropped two lead balls from a church tower in Delft and printed the result in 1586, the same year. Stories drift towards the famous name. That is why we weigh witnesses rather than count pictures.