Translation © George MacDonald Ross, 1998–1999
The Assayer, in which are weighed with a fine and accurate balance the contents of the
Astronomical and Philosophical
of Lothario Sarsi of Siguenza, written in the form of a letter to the Illustrious and Very Reverend
Monsignor Don Virginio Cesarini, Lincean Academician, and Chamberlain to his Holiness, by Signor Galileo Galilei,
Lincean Academician, Gentleman of Florence, and Chief Philosopher and Mathematician to the Most Serene Grand Duke
of Tuscany (Rome, Giacomo Mascardi, 1623).
This document is approximately 4 sides of A4.
[The Language of Nature]
. . . .  I seem to detect in Sarsi a firm belief that, in philosophising, it is necessary to depend on the opinions of some famous author, as if our
minds should remain completely sterile and barren, when not wedded to the reasonings of someone else.  Perhaps he thinks that philosophy
is a book of fiction written by some man, like the
— books in which the least important thing is whether what is
written there is true. Mr. Sarsi, this is not how the matter stands. Philosophy is written in this vast book, which continuously lies upon before
our eyes (I mean the universe). But it cannot be understood unless you have first learned to understand the language and recognise the characters
in which it is written. It is written in the language of mathematics, and the characters are triangles, circles, and other geometrical figures.
Without such means, it is impossible for us humans to understand a word of it, and to be without them is to wander around in vain through a
dark labyrinth. . . . .
[Primary and Secondary Qualities]
. . . .  It now remains for me to fulfil the promise I made Your Excellency above, and give you certain thoughts of mine about the
proposition ‘Motion is the cause of heat,’ showing how it seems to me possible that it is true. But first I need to give some consideration to
what it is that we call ‘heat’, since I strongly suspect that the concept which everyone has formed of it is very far from the true one. People have
come to believe that it is a genuine accident, affection, or quality, which inheres as something real in the matter which we feel ourselves being
warmed by. Nevertheless, I say that, as soon as I conceive of a piece of matter, or a corporeal substance, I feel myself necessarily compelled
 to conceive along with it, that it is bounded, and has this or that shape; that in relation to some other body it is either small or large; that it
is in this or that place, and in this or that time; that it is in motion or at rest; that it either touches or does not touch some other body; and that it
is one, few, or many; nor can I separate it from these states by any act of the imagination. But I do not feel my mind forced to conceive it as
necessarily accompanied by such states as being white or red, bitter or sweet, noisy or quiet, or having a nice or nasty smell. On the contrary, if