**Guidobaldo del Monte** was an Italian mathematician who wrote on statics and also on perspective and astronomy.

- We should notice at this point that he signed himself Guidobaldo dal Monte (using 'dal' rather than 'del' as was fairly common at the time) so it is not unusual to see him referred to as Guidobaldo dal Monte rather than Guidobaldo del Monte.
- For convenience, however, we will refer to him as Guidobaldo throughout this article, although in other places in this archive we refer to him as del Monte.
- Guidobaldo studied mathematics at the University of Padua in 1564.
- Guidobaldo may have known Tasso before they studied at Padua together, for Tasso was almost exactly the same age as Guidobaldo and had been educated at the court of the Duke of Urbino, with the duke's son, from 1556.
- For a while Guidobaldo served in the army during the war against the Ottoman in Hungary.
- After serving in the army, Guidobaldo returned to his estate of Montebaroccio in Urbino where he was able to spend his time doing research into mathematics, mechanics, astronomy and optics.
- Guidobaldo's book Liber mechanicorum (1577) was regarded as the greatest work on statics since Greek times.
- It was a return to classical Greek rigour deliberately rejecting the approach of Jordanus, Tartaglia and Cardan.
- Another error that Guidobaldo makes is to accept an argument of Pappus on inclined planes over that of Jordanus, which is in fact correct.
- We should not be too critical, however, for much of Guidobaldo's book is excellent material which would be accepted by Galileo and form the basis for his major step forward.
- For example Guidobaldo shows that systems of pulleys can be reduced to problems with levers with some excellent analysis.
- As we have indicated, much of Guidobaldo's approach was adopted by Galileo who was his friend for 20 years.
- Interesting in this respect is an experiment on projectiles which Guidobaldo carried out.
- While we are discussing Guidobaldo and Galileo, we should note that as well as giving Galileo financial support, Guidobaldo supported him for the professorship of mathematics at the University of Padua in 1592.
- Guidobaldo's treatise six books on perspective Perspectivae libri sex, published in 1600, contains theorems which he deduced with frequent references to Euclid's Elements.
- The most important result in Guidobaldo's treatise was that any set of parallel lines, not parallel to the plane of the picture, will converge to a vanishing point.
- Guidobaldo also wrote on refraction in water but it was unpublished on his death.
- Interested in machines of many different types, Guidobaldo wrote on the Archimedean screw to raise water.
- In particular Guidobaldo, together with his teacher Commandino, improved the reduction compass, helping develop it into the proportional compass.
- Up to now the main source of information about this question was the Preface to the treatise "Del compasso polimetro of the Urbino mathematician Muzio Oddi".
- The next step forward from the efforts of Commandino and Guidobaldo was that of Galileo in 1606 when he developed the proportional compass into a type of slide-rule.

Born 11 January 1545, Pesaro (now Italy). Died 6 January 1607, Montebaroccio (now Italy).

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Astronomy, Geometry, Origin Italy

**Oâ€™Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive