Where are Sunspots? The Practical Method of Galileo as an example of Mental Model

After the publication of Sidereus Nuncius, in the controversy with Ch. Scheiner, Galileo developed several arguments on behalf of the hypothesis that sunspots are contiguous to the surface of the Sun, and presented them in his Istoria e dimostrazioni intorno alle macchie solari e loro accidenti (Rome 1613). One of them, named by Galileo a Practical Method, advocates very clearly the correctness of the hypothesis. In the paper the method in question is briefly described. It is argued that the Practical Method is not a thought experiment, but rather a mental model proposed precisely in order to solve the problem of sunspots’ location.