We had a small group this month and I'm sure that's because a number of people didn't want to come because they hadn't finished the book. I'll admit right now that I didn't finish the book either. I started too late and ran out of time.
To some extent I believe that the book's title is a bit of false advertising. The book really isn't about Galileo's daughter (this may be because of the lack of information about Virginia). It's about Galileo himself and his relationship with his family. The book opens with a letter from Virginia to her father, but then it takes one hundred pages before she appears as a player again. In the meantime, the narrative is focused on Galileo. There is discussion of his relationship to the children's mother, their births, and his attempts to get Virginia and her sister placed in a convent as wards, but other than that the girls don't appear much at all.
Apparently in the second half of the book, the narrative is more evenly focused (with more frequent appearances of Virginia's letters), but I didn't get far enough to see that for myself. At this point I don't feel like I need to finish the book. I've placed it in Russell's to-be-read pile because I think that he'll like it, interested as he is in Galileo, astronomy, history of science, and the Catholic church.
