Galileo’s Daughter: A Drama of Science, Faith and Love. Dava Sobel

to determine whether Pietro injured Giovanni last night, but not whether Giovanni was injured, since the judge can see that for himself. But even in conclusions which can be known only by reasoning, I say that the testimony of many has little more value than that of few, since the number of people who reason well in complicated matters is much smaller than that of those who reason badly. If reasoning were like hauling I should agree that several reasoners would be worth more than one, just as several horses can haul more sacks of grain than one can. But reasoning is like racing and not like hauling, and a single Barbary steed can outrun a hundred dray horses.

      It took Galileo two years to complete The Assayer, beset as he was throughout by many family and official matters. Marina Gamba died in February 1619, leaving Galileo’s children officially motherless. Having helped both his daughters take the veil, Galileo now atoned for the messy circumstances of his son’s birth by getting Grand Duke Cosimo II to legitimise Vincenzio on 25 June, two months before the boy’s thirteenth birthday. Cosimo handled this matter-of-factly enough, knowing his own Medici forebears to have fathered at least eight illustrious illegitimate sons, two of whom had become cardinals – and one of those had traded the cardinal’s biretta for the pope’s tiara as His Holiness Clement VII.

      Meanwhile Galileo’s mother, Madonna Giulia, grew older and ever grouchier at the house in Florence where she had stayed when her son moved to Bellosguardo. ‘I hear with no great surprise that our mother is being so dreadful,’ Galileo’s brother, Michelangelo, commiserated in October 1619 from the safe distance of Munich. ‘But she is much aged, and soon there will be an end to all this quarrelling.’