Eustachio Divini

So Eustachio began his new fertile formative experience with people of his same generation such as Evangelista Torricelli, Giovanni Alfonso Borelli, Bonaventura Cavalieri and Michelangelo Ricci.

The Court of Medici in Florence bought many Divini's telescopes and was not only a test bench for him, but also a spreading engine for the notoriety of the optician, because of the role of the associated Accademia del Cimento in triggering astronomical research in all Europe.

So it isn't a surprise that the prestigious Science Academy of London dedicated to Divini with the inscription: "Divinus Eustachius De Sancto Severini, Insignis Mathematicus".

A copy of that selenography was given later by Eustachio Divini to his hometown San Severino, his birth town he kept in touch continuously together with his brother Cipriano, a well-established painter in Rome.

These discoveries had permitted previously to argue out the rotation of Jupiter around its axis, whereas Divini was able to demonstrate the amateurs and astronomers community that his instruments were as effective as the ones made by his rivals, Campani brothers, manufacturer of telescopes for Cassini.

And he was the most honest of all competitors because of his fair and humble nature that prevented him to defraud the tests or to put forward mysterious (as much as sham) theoretical reasons, supposedly based on the laws of optics, to praise his lenses and instruments, as was done by more famous scientists.

Divini's reputation as the best European maker of telescopes begun to be superseded in 1656, when Christiaan Huygens announced the discovery of a "moon" of Saturn (the satellite that was called Titan later on).

The Dutch astronomer, discovered it in 1655 using his own telescopes, then followed its movements for months, seeing the satellite make a complete revolution of Saturn "arms" every sixteen days.

[14] We can interpret Huygens' worry to attribute his discovery to a visual fact as a sort of pre-defensive attitude, demonstrating that any change of the heavens based on the strongest logical reason, was still hampered by the Inquisition in that post-Galilean age.

So Huygens, in his memorial dedicated to Prince Leopold of Medici,[15] suggested that the previous wrong interpretations as "opposite bodies" or "handle like formations" of Saturn ring were due to the inferior quality of the instruments.

But Fabri imposed on Divini by making an issue out of Huygens' avowed Copernicanism, imagining a number of light and dark satellites moving behind the planet in tight formation, in such a way to reproduce the appearance of the anses.

[24] In the meanwhile Prince Leopold had built models of both hypotheses by Fabri's and Huygens' and had the academicians of Cimento observed them lighted from a distance, to decide which one was more adequate to explain Saturn's appearances.

In the paragone of April, 30th 1664 Divini used a telescope manufactured by him with a very complex optical system and previously sold to the nephew of Pope Alexander VII, Cardinal Flavio Chigi, for a very high price.

In 1665 the Grand Duke Ferdinand II and Prince Leopold acquired a number of Campani and new Divini telescopes and subjected them to tests of their own in astronomical observations.

Both the antagonists proposed to the Accademia del Cimento an impartial test based on the manufacturing of the best objective lenses with given curvature starting from the same piece of glass divided in two parts.

Divini, resigned to leave the top position of his art to the antagonist, wrote with pride in 1666: "my glasses have lost nothing in these paragoni, in fact after the contest and even today I have new orders from Florence" (from letter to C. A. Manzini).

[29] The Technical Institute of San Severino Marche was named after the scientist Eustachio Divini in 1983, on the occasion of renewed historical studies on his scientific and technological development.