Lenses and Waves

54 CHAPTER 3
discovered since Galileo. 2 The tract ended with an anagram holding
Huygens’ second discovery: the true nature of the inexplicable appearance of
Saturn. Three years later, he elaborated his explanation in Systema saturnium.
The strange attachments to the planet that disappeared from time to time
were manifestations of a solid ring around the planet. 3
He owed much to his instruments, Huygens wrote in Systema saturnium.
He prided himself on his practical skills of telescope making and claimed that
his success proved the unmatched quality of his telescopes. Van Helden
explains that his discovery owed at least as much to his talents for
geometrical and physical reasoning. 4 Initially, Huygens had used a 12-foot
telescope of their own make. After a trip to Paris, where he probably
discussed his observations, the brothers built a new, 23-foot telescope which
he started using in February 1656. 5 He illustrated the difference between
both pieces in Systema saturnium (Figure 21). Everyone could see for himself
that Huygens could hold his own with the best of telescope makers. At least,
that is how he saw it himself. His boasting offended Eustachio Divini in
Rome, who saw his fame of being the best telescope maker in Europe
challenged. In 1660 he published Brevis annotatio in systema saturnium, disputing
the observational results as well as Huygens’ claims regarding his
instruments. 6 The tract was actually written by the Roman astronomer Fabri.
In the ensuing dispute Divini/Fabri were no match for Huygens, at least not
as regards the structure of the system of Saturn. 7
Figure 21 Observations of Saturn with the 12- and a 23-foot telescope.
The dispute itself is less interesting than the fact that Huygens did not feel
above at entering a dispute with a craftsman. It raises questions about the
relationship between his theoretical and his practical pursuits, how he valued
his mathematical expertise and his skilful craftsmanship. The last part of this
2
Huygens did not name it, he called it ‘saturni luna’ and sometimes ‘comes meus’. The name Titan was
given by Herschel in 1847.
3
OC15, 296-299.
4
Van Helden, “Huygens and the astronomers”, 150-154. Van Helden, “Divini vs Huygens”, 48-50.
5
OC15, 177; 230. Huygens employed Rhineland feet (0,3139 meters) and inches (0,026 meters).
6
It is reprinted in OC15, 403-437.
7
Van Helden, “Divini vs Huygens”, 36-40.