In June of 1606 Galileo had printed at his home in Padua, by the printer Pietro Marinelli, 60 copies of Le operazioni del compasso geometrico e militare. Each booklet was sold along with one of the instruments whose numerous applications it described. Perhaps for the purpose of preventing any plagiarism of his invention, Galileo failed to explain how the proportional lines were constructed.
The text is prefaced by a Dedica (Dedication) to the young Prince Cosimo de' Medici (1590-1621), whom Galileo personally instructed in the use of the compass, and by a Proemio ai Lettori (Preface to Readers) in which the scientist revealed important details of his invention.
Read the whole text or download it onto your computer.