~ Shop ~




A unique, previously unrecorded letter by the Italian cartographer and scientist Giovanni Rizzi-Zannoni with his measurements of the latitude of Istanbul, based on the suggestions personally received from a Dalmatian geographer Roger Boscovich during his stay in Istanbul to observe the Transit of Venus in 1761.

1 in stock


This unique, previously unrecorded letter was written by an Italian cartographer Giovanni Rizzi-Zannoni to a Venetian Ambassador, Piero Correr, in Istanbul on February 30, 1863, and includes his recent measurements of the latitude of Istanbul, based on the latest advice he received from his colleague, the geographer Roger Boscovich.
According to the letter, Rizzi-Zannoni, who at the time lived in Istanbul, met Boscovich, when this Dalmatia-born scientist visited the city to observe the Transit of Venus at the behest of the Royal Society, in 1761. Boscovich arrived to the city too late for observations and spent most of his time in Istanbul ill. 

According to the letter, Boscovich suggested Rizzi-Zannoni to precisely measure the meridian of Constantinople, and the positions of the eclipses of Moons of Jupiter, the so-called Jovian method. 

Rizzi-Zannoni includes measurements of the eclipses, which he took on October 13, 1762, and quotes the newly measured latitude of Istanbul, which was with 41° 2’ 27’’ very close to the one we know today – 41° 00’ 49’’. At the end of the letter Rizzi-Zannoni asks the recipient to keep the new discoveries a secret. 

Correctly determining the geodetic location of Constantiople was especially important.  It was not only critical to understanding the geography of one of the World’s most strategically important cities, but, moreover, Constantinople’s role as the gateway to the East and its place on the extreme southeastern tip of Europe ensured that it was one of the anchors, or seminal basepoints, for constructing regional and general maps of Europe and the Near and Middle East. 

The letter is not only important, because it gives new scientific information, but it also offers a valuable insight in the correspondence of scientists in the Enlightenment Age.

The date on the letter also records Rizzi-Zannoni’s until now mysterious staying in Istanbul, which is only vaguely mentioned in his own writings, where he claimed he spent some time in the Ottoman capital during the ambassadorship of Charles Gravier, comete de Vergennes (served between 1774 – 1787). (Mary Sponberg PEDLEY. Rizzi Zannoni in Paris and the Culture of French Cartography. In: Giovanni Antonio Rizzi Zannoni. Scienziato del Settecento veneto, Venice 2015, p. 87).


Giovanni Rizzi-Zannoni

Giovanni Rizzi-Zannoni (1736 – 1814) was one of the most consequential cartographers of the Enlightenment Age.  Born in Padova, Italy, he studied at that city’s legendary university, before embarking on a voyage to Turkey and Russia.  

In 1753, he became an official geographer to the King Augustus III of Poland and participated on surveys that eventually led to the first broadly accurate general map of that country, authored and published by Rizzi-Zannoni as the Carte de la Pologne: divisée par provinces et palatinats (1772).  In the mid-1750s, he gained direct experience with the region in question when he worked a surveyor for the Counties of Oldenburg and Delmenhorst.  He fought on the Prussian side at the beginning of the Seven Years’ War, but was captured by French forces in 1757.  Transported to Paris, Rizzi-Zannoni’s abilities as a geographer were greatly admired, and in return for his freedom and good treatment, he accepted an offer to work for the French government, eventually rising to the lofty position of Premier hydrographe du Dépôt des cartes et plans de la Marine (1772-5).  It was during his time in French official employ that he made the present map.  In 1776, Rizzi-Zannoni returned to Padova and henceforth concentrated his efforts on mapping Italy.  

His monumental map of the Kingdom of Naples, published as the Atlante geografico del Regno di Napoli (Atlas géographique du Royaume de Naples) (1789-1812), is considered to be one of the greatest masterpieces of cartography of the Enlightenment era.


Roger Boscovich: Enlightenment Polymath

Roger Joseph Boscovich (Croatian: Ruđer Josip Bošković) was a great Enlightenment era polymath, whose work and theories were decades ahead of their time.  He was variously responsible for groundbreaking contributions to atomic theory, physics, geodesy, gravitational theory and astronomy, amongst several other disciplines.  One will also notice that Boscvich moved around a great deal for someone of his time.  This is thought to be largely due to his incredibly difficult temperament.  While institutions were initially honoured to welcome such an esteemed scientist, they soon grew tired of his imperious and argumentative nature.  It was often not long before they encouraged him to ‘broaden his horizons’ somewhere else.

Boscovich was born in the Republic of Ragusa (today’s Dubrovnik, Croatia) in 1711, the son of a wealthy merchant.  He was a precocious student and trained towards entry into the Jesuit Order.  He moved to Rome, where he passed his novitiate, followed by further study at the Collegium Romanum.  His brilliance in science and mathematics astounded his colleagues and he was appointed full professor of mathematics at the college in 1740. 

Boscovich was a workaholic who, in addition to fulfilling his professorial duties, was able to dedicate vast resources towards illuminating a variety of scientific questions.  He first gained widespread notice in the astronomy community by proposing a solution for locating the Sun’s equator, by measuring the velocity of the star’s rotation through monitoring the spots on its surface.  He also investigated the Aurora Borealis, the Transit of Mercury, the shape of the Earth, the theory of comets, the law of continuity, inconsistencies in gravitation, and the more accurate mathematical quantification of telescopic observations, amongst many other topics.  No problem, no matter how difficult, seemed too intimidate his restless mind. 

In 1742, Pope Benedict XIV summoned a group of experts, including Boscovich, to come up with a solution to a growing problem: the dome of St. Peter’s Basilica was cracking.  While not an engineer, it was Boscovich who propose the remedy: strengthening the dome with custom iron rings.  This endeared Boscovich to the pope, who would become an enthusiastic patron of the Croatian Jesuit. 

Boscovich’s next great endeavour was his aforementioned project with Christopher Maire to measure the Rome-Rimini meridian, from 1750 to 1753, resulting in the De Litteraria Expeditione (1755).

During the late 1750s, Boscovich spent quite a bit of time in Laibach, Inner Austria (modern Ljubljana, Slovenia), where he developed a scientific curriculum for the Jesuit College.  His syllabus became highly consequential, as it gave rise to a new generation of scientists, including Carl Sheiffer, Jurij Vega and Gabriel Gruber. 

Boscovich soon moved on to an entirely different subject, immersing himself in the composition of matter.  His resulting treatise on atomic theory, Theoria philosophiae naturalis (Vienna, 1758), is widely considered to be his most brilliant work, generations ahead of its time.

Curiously, while Boscovich was described as a difficult character, he had a good record as a diplomat.  He successfully represented Lucca in a dispute against Tuscany, and this success prompted his native Republic of Ragusa to select him for a sensitive mission.  During the early period of the Seven Years’ War (1756-63), Britain accused Ragusa of lending aid to French shipping, in violation of Ragusa’s declared neutrality.  The situation had to be urgently defused, as, if it so chose, the Royal Navy could effortlessly thrash the tiny republic.  In 1760, Boscovich headed to London and managed to convince the British that the reports of a Franco-Ragusan alliance were mere fiction.  

While in London, Boscovich was feted by the scientific community, which was very much in admiration of his work.  He was elected as a fellow of the Royal Society and made numerous valuable contacts.  In 1761, at the behest of the Society, Boscovich travelled to Istanbul to observe the Transit of Venus.  From there, he completed an odyssey through Bulgaria, Moldavia and Poland to St. Petersburg, where he was elected to the Russian Academy of Sciences.

Boscovich next appears in the joint role as the chair of mathematics at the University of Pavia and the director of the Brera Observatory.  Upon the global Suppression of the Jesuit Order in 1773, Boscovich avoided the terrible fate of imprisonment and disgrace suffered by many of his brethren.   He somehow managed to be appointed as Director of Optics of the French Navy, and he repaired to Paris where he enjoyed the very large annual salary of 8,000 livres.  In 1783, Boscovich returned to the Milan area, where he died in 1787.  His legacy far outlived him, as scientists in numerous fields were inspired by his work for decades thereafter.

Additional information


Place and Year