Il Saggiatore

The Assayer (Italian: Il Saggiatore) was a book published in Rome by Galileo Galilei in October 1623 and is generally considered to be one of the pioneering works of the scientific method, first broaching the idea that the book of nature is to be read with mathematical tools rather than those of scholastic philosophy, as generally held at the time.

The context of the essay was to reply to the treatise Libra astronomica ac philosophica of 1619 by Orazio Grassi, a Jesuit mathematician at the Collegio Romano, which used the pseudonym of Lotario Sarsi Sigensano. The debate between Galileo and Grassi started in 1618, when the latter published Disputatio astronomica de tribus cometis anni MDCXVIII, in which he asserted that comets are celestial bodies. Grassi adopted Tycho Brahe's Tychonic system, in which the other planets of the solar system orbit around the sun, which, in turn, orbits around the earth. In his Disputatio Grassi referenced many of Galileo's observations, such as the surface of the moon and the phases of Venus, without mentioning him. Grassi argued from the apparent absence of observable parallax that comets move beyond the moon. Galileo mistakenly believed that comets are an optical illusion.

In 1616 Galileo may have been silenced on Copernicanism. In 1623 his supporter and friend, Cardinal Maffeo Barberini, a former patron of the Lynx and uncle of future Cardinal Francesco Barberini, became Pope Urban VIII. The election of Barberini seemed to assure Galileo of support at the highest level in the Church. A visit to Rome confirmed this. The Assayer is a milestone in the history of science: here Galileo describes the scientific method, which was quite a revolution at the time, given the prevalence of scholasticism, which, instead of relying on the observation of nature to make assumptions, relied heavily on ipse dixit.

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