Giovanni Poleni

When a great genius appears in the world you may know him by this sign; that the dunces are all in confederacy against him.
Jonathan Swift

Giovanni Poleni
Giovanni Poleni (1683-1761)

In 1709 the young professor of astronomy, meteorology, and mathematics and Marquis of the Holy Roman Empire Giovanni Poleni published his first book—Miscellanea, a small collection of dissertations on physics (it was a sort of doctoral thesis to obtain the University appointment). Miscellanea includes dissertations on barometers, thermometers, and conical sections in sundials, as well as an illustrated treatise describing his arithmetical calculating machine, which proved to be the first calculating machine with gears with a variable number of teeth (so-called pin-wheel). It seems Poleni commenced his work on the calculating machine in 1707, having heard the news of Pascal’s and Leibniz’s calculators from scholars in person and from their writings and, though having no drawings nor technical description of the two previous inventions, decided to design and build an original one.

The second section of the Miscellanea describes the calculating machine of Poleni. The chapter opens with the following words:
“Having heard several times, either from the voice, or from the writings of scientists, which were made by the insight and the care of the most illustrious Pascal and Leibniz, two machines which are used for arithmetic multiplication, which I do not know the description of the mechanism, and I do not know if it was made manifest, I wanted and guess with thought and reflection to their construction, to build a new one that implements the same purpose.”

Poleni Miscellanea
The calculating machine of Poleni (the drawing in Miscellanea)

Then Poleni continues: “By a happy chance, I designed a machine with the use of which even a novice in the art of calculation, provided that knows the figures, can perform arithmetic operations with his own hand. So I am worried that it was made of wood, as I had planned and that, although initially built with poor precision, showed that this was achievable, rather than made. Therefore, I have recreated the machine from scratch, building it of the hardest wood, with all possible attention and the work done has not failed in vain.”

So, according to the inventor himself, two wooden copies of the machine were made, but unfortunately, none of them survived to the present time. The image below shows a replica of the machine from 1959.

A replica of the calculating machine of Poleni (© Museo Nazionale della Scienza e della Tecnica, Milan)
A replica (made in 1959) of the calculating machine of Poleni (© Museo Leonardo da Vinci, Milan)

A description of the Poleni’s machine appeared in 1727 in Jacob Leupold’s Theatrum arithmetico geometricum and in “Versuch einer Geschichte der Rechenmaschine” by Johann Bischoff, 1804.

One of the first biographers of Poleni, the Frenchman Jean de Fouchy Pajil Grandjean, claims in his 1762 book “Eloge de Jean POLENI, Marquis du St. Empire, (né 1683 mort 1761)”, that …having heard that Mr. Brawn, a famous mechanic in Vienna, presented a similar machine to the Emperor, Poleni destroyed his machine and no more wanted to rebuild it. The same story is repeated in the two later Poleni’s biographies—Pietro Cossali (1813), and Giuseppe Gennari (1839). Despite the fact, that Fouchy was in strict contact with Poleni (when alive) and knew him personally, this story is quite questionable, not only because it is not compatible with the gentle character of Poleni. Fouchy obviously mentioned the German mechanic, constructor, and optician Anton Braun, who worked in Vienna for the court and really presented his calculating machine (based on the pin-wheels of Poleni and Leibniz) with great success to the Emperor, but this happened as late as in 1727. It is possible Braun had gotten information about Poleni’s machine (we know that Braun worked under the supervision of the imperial engineer Johann Jacob Marinoni, who was in correspondence with Poleni and perhaps visited him in Venice), and had decided to use the idea of Poleni in his construction, the history of inventions is full of cases like that. In fact, if Poleni hadn’t managed for almost 20 years to manufacture and demonstrate a working copy of his machine, obviously he was not interested in this device at all and fully deserved to be outrun by others.

The machine of Poleni was quite big (with the dimensions of a big clock with a pendulum). Let’s examine its mechanism, looking at the illustration from the Theatrum arithmetico geometricum.

The calculating machine of Giovanni Poleni, a part of illustration from the Theatrum arithmetico geometricum
The calculating machine of Giovanni Poleni, a part of the illustration from the Theatrum arithmetico geometricum

The mechanism is set in motion by means of the weight K, tied to the end of the rope l, which is winded over the cylinder t. The most important element of the machine—the so-called pin-wheel, invented probably (it is known that Leibniz has a similar design in one of his manuscripts and that Leibniz and Poleni had a correspondence) by Poleni, is placed to the right of the axis VY. Actually in the machine are placed 3 pin-wheels, which means, that the input mechanism has only 3 digital positions.

The pin-wheel of Poleni actually is a smooth wheel, with attached to it a sector with 9 blocks, illustrated in the right part of the figure. Each block contains a body (marked with 3 in the figure), a tooth (marked with 2), and a small rod (marked with 4). There is also a fourth element of the block—a small spring, which is not shown in the figure. In the assembled block (marked with 1), the tooth can be erected outside of the block, if the rod is pressed by the operator or hidden in the body of the block if the rod is released. Thus in each one of the three sectors with blocks can be set from 0 to 9 erected teeth. When the tooth is erected, it will engage with the calculating mechanism during the revolution of the calculating mechanism, otherwise—not.

The output mechanism consists of six dials, i.e. it has six digital positions. The tens-carry mechanism uses a one-tooth wheel and obviously has not been designed well, because it caused problems (it can happen that the machine stops in the middle of a tens-carry step due to adverse leverage forces.)

An additional crank was used for shifting the pin-wheel mechanism by one place at a time with respect to the transfer tooth wheels, thus allowing the multiplicand to be multiplied by the multiplier in higher places.

As a whole, despite the innovative idea of Poleni for the pin-wheel, which would become an extremely popular constructive element of calculating machines some 150 years later (see the machines of Baldwin and Odhner), his machine looks rather rough and ill-formed device, as compared to the machine of his successor—Anton Braun.

The calculating machine of Giovanni Poleni, the whole illustration from the Theatrum arithmetico geometricum
The calculating machine of Giovanni Poleni, the whole illustration from the Theatrum arithmetico geometricum

Biography of Giovanni Poleni

Giovanni Poleni was born on 23 August 1683, in Venice (most probably in the Palazzetto, still sitting projected onto the Grand Canal, see the photo below). He was the only son of Jacopo (Giacomo) Poleni (1655-1737) and Elisabetta Broiuola (or Brugnol, Brajola, or Brogiola). Jacopo Poleni was a well-educated “middle class” Venetian, a literate and a poet, but searching for glory, in early 1683 he entered as a volunteer in the army of Emperor Leopold I and in the same year’s autumn, he took part and displayed a lot of courage in the battles against Turks during the Siege of Vienna, and in Hungary. In June of 1685, the Emperor awarded him for his merits with the titles “Marquis, Count of St. Michael the Archangel, and Knight, along with his descendants”, a title, confirmed by the Senate in July 1686. So, only two years old, Giovanni Poleni became a Marquis, what a remarkable beginning of his life 🙂

Palazzetto Pisani in Venice Poleni
Palazzetto Pisani in Venice, a property of the Poleni family until 1751, when Giovanni Poleni sold it to Andrea Pisani

As a young man, Giovanni showed brilliance in a wide variety of different subjects and it was clear that he was extraordinarily talented. His parents encouraged him to begin a judicial career but, after being introduced to mathematics and experimental science (following the works of René Descartes) by his father, it became clear that he had now found the subjects which gave him the most satisfaction.

In 1695 Poleni began his studies in the school of the Basilica Santa Maria della Salute in Venice, where he studied letters (under the guidance of Padre Stanislao Santinelli), philosophy and theology (under Padre Francesco Caro), civil and military architecture, drawing, painting, and perspective (under the painter Giuseppe Marcati). In 1707 Poleni began to deal with physics, carrying out the first scientific experiments. In the same year, he met Giovanni Battista Morgagni, the anatomist, regarded as the father of modern anatomical pathology, with whom Poleni started a friendship and collaboration that continued until his death.

At the end of 1709, Poleni accepted the chair of Astronomy and Meteorology at the University of Padua, and in February 1710, he moved with his family to Padua. For over 40 years he kept outstandingly accurate meteorological records which have proved invaluable to later scientists. In 1709 he published his first book—Miscellanea: de barometris et thermometris; de machina quadam arithmetica; de sectionibus conicis in horologiis solaribus describendis, a collection of dissertations on physics.

University of Padova
The University of Padova is one of the world’s oldest centers of higher learning, founded in 1222

In 1715 Poleni became a professor of physics, in addition to holding the chair of astronomy and meteorology, and was invited by the Venetian Senate to investigate the problem of hydraulics relating to the irrigation of Lower Lombardy. He was appointed to the chair of mathematics at Padua in 1719 which had been vacated by Nicolaus Bernoulli. In 1717 he published a major treatise on hydraulics and hydrodynamics—De motu aquae mixto libri duo, which describes estuaries, ports, and rivers.

In 1710 Poleni was elected a fellow of the Royal Society of London, upon a proposal by Sir Isaac Newton. In 1715 he was honored by being proposed by Gottfried Leibniz, a correspondent of him, for election to the Berlin Academy of Science in 1715. In 1723 he was admitted to the Academy of the Institute of Sciences of Bologna. In 1724 he was appointed a partner of the newly founded Saint Petersburg Imperial Academy, starting his correspondence with Leonard Euler. In 1739, the prestigious Académie Royale des Sciences of Paris admitted him among its members.

Poleni observed the solar eclipse in 1724 and wrote a treatise on the topic which was published the following year. From 1739 he taught experimental physics since by this time he had a physics laboratory. It was the first physics laboratory to be established in an Italian university.

In 1729, Poleni built a tractional device that enabled logarithmic functions to be drawn. In 1743 he was invited by the Pope and made a significant contribution to the consolidation of San Pietro’s dome in Roma.

Poleni was appointed to the chair of Nautical Studies and Naval Construction at Padua in 1756. From this time he taught nautical sciences and shipbuilding. A music-lover, Poleni was the patron of Giuseppe Tartini (1692-1770)—a famous composer and violinist.

On 30 December 1708, obeying his father, Giovanni Poleni married Orsola Roberti (1686-1737), who was from a high-ranking and noble Bassano del Grappa family. The family had six children, five boys, and a girl. The firstborn was Jacopo (Giacomo), a very talented boy, born on 18 October 1709, and died in 1747. All of the boys of Poleni pursued a religious career, with the exception of the last, Eugenio (1717-1736), who was destined to give succession to the family but died only 18 years old, to the severe grief of Marquis Giovanni, who in 14 months lost three dearest people—his son, his wife, and his father. Poleni had three other sons: Bernardo, Luca, and Francesco, and one daughter—Elisabetta, who married the botanist professor Giulio Pontedera.

Giovanni Poleni, who since the 1720s had suffered from violent headaches due to an accident, died in Padua on 15 November 1761, after a few days of rapid worsening. The autopsy, performed by his colleague and friend Giambattista Morgagni, a famous anatomist, revealed that the death had been caused by an aortic aneurysm.

Giovanni Battista Morgagni, а long standing friend, colleague, and doctor of Giovanni Poleni
Giovanni Battista Morgagni (1682–1771), а long-standing friend, colleague, and doctor of Giovanni Poleni