Huygens and Titan, Saturn’s moon

On 25 March 1655, Huygens discovered a moon orbiting the planet Saturn, using a telescope lens he had ground himself. Christiaan initially formulated his discovery in the form of an anagram: a rearranging of the letters to hide the original meaning of his Latin sentence. By making his discovery known to a few correspondents in this manner, Huygens safeguarded his claim to the discovery, while allowing himself the time to test his theories by observing Saturn for longer.

Christiaan used a line of verse by the Roman poet Ovid for his anagram: ‘ADMOVERE OCVLIS DISTANTIA SIDERA NOSTRIS’, with an additional string of unconnected letters VVVVVVVCCCRRHNBQX’. The translation of the first section is: ‘They brought the distant stars closer to our eyes’. As Christiaan himself said: ‘Nobody saw before me, what was hidden in these letters’.

Huygens revealed the real meaning of this anagram a year later, in March 1656, in a small printed pamphlet entitled DE SATURNI LUNA OBSERVATIO NOVA and in some letters to his correspondents. The text of the pamphlet was also included in Pierre Borel’s book about the discovery of the telescope (De vero telescopii inventore), which appeared later that month.

The correct reading of the anagram is ‘SATURNO LUNA SUA CIRCUNDUCITUR DIEBUS SEXDECIM HORIS QUATUOR’, which can be translated as ‘Saturn’s moon circles the planet in sixteen days and four hours’.

Christiaan was so pleased with this discovery that he used a diamond to engrave the first lines of the anagram around the edge of the object lens (objective) he used to discover the planet. This lens can still be viewed today. It was found by chance in 1867 among a number of antique instruments at Utrecht University. This ‘Admovere’ lens is now in the Utrecht University museum.