Writing to his friend Don Virgilio Cesarini, Galileo complains of the “ill feeling” and “stubborn opposition” that have come against him and his scientific writings. Critics don’t seem to realize that Galileo’s findings come from the plain evidence of the senses, which they can see for themselves. Some jealous scientists, such as Simon Mayr, even tried to appropriate Galileo’s discoveries as their own. Most recently, a person calling himself “Lothario Sarsi” attacked Galileo in print in response to Galileo and Mario Guiducci’s work “Discourse on Comets.” While Galileo at first resolved to ignore these attacks and maintain a peaceful frame of mind, their persistence compelled him to speak out.

These are the main points that Galileo makes in reference to Sarsi:

- Sarsi relies on authority in philosophy and science. Instead, Galileo insists that experience and reason are the proper guides to the truth.

- Sarsi disparages Galileo’s theories because they have historically had few followers. Galileo responds that the number of people who understand true science and philosophy is small, while “the crowd of fools who now nothing…is infinite” (239).

- Sarsi criticizes Guiducci’s statement that the telescope magnifies objects to an infinite degree. Galileo shows that this is mere sophistry and quibbling over words, because “infinite” is used here in a relative sense (241-42).