  The trial and condemnation of Giordano Bruno was mainly based on arguments of
philosophical and theological nature, and therefore different from Galilei's.
Such elements contribute to unfairly devalue the scientific contribution of
Bruno and do not properly account in particular for his contribution to
physics. This paper discusses the contribution of Bruno to the principle of
relativity. According to common knowledge, the special principle of relativity
was first enunciated in 1632 by Galileo Galilei in his Dialogo sopra i due
massimi sistemi del mondo (Dialogue concerning the two chief world systems),
using the metaphor today known as "Galileo's ship": in a boat moving at
constant speed, the mechanical phenomena can be described by the same laws
holding on Earth. We shall show that the same metaphor and some of the examples
in Galilei's book were already contained in the dialogue La cena de le Ceneri
(The Ash Wednesday Supper) published by Giordano Bruno in 1584. In fact,
Giordano Bruno largely anticipated the arguments of Galilei on the relativity
principle. It is likely that Galilei was aware of Bruno's work, and it is
possible that the young Galilei discussed with Bruno, since they both stayed in
Venezia for long periods in 1592.
