The calculating machine of Giovanni Poleni

The professor of astronomy, meteorology and mathematics and Marquis of the Holy Roman Empire Giovanni Poleni (1683-1761) (biography) was one of the famous european scientists of the beginning of the 18th century.

In 1709 the young professor 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. It 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). In the description of the Poleni's machine in the Leupold's Theatrum arithmetico geometricum is said that the machine was ... based on reports that Poleni had received of those of Pascal and Leibniz. Poleni actually built this machine which was reportedly very simple and easy to operate; but when he heard of another machine presented to the Emperor by the Viennese mechanician Brauer, he destroyed his own and never rebuilt it.

This story is quite questionable. Leupold 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 unbelievable, that Poleni needed 18 years (from the publication in 1709 to the 1727), in order to manufacture his machine. Actually there is information, that Poleni manufactured two wooden copies of his machine, and one of them survived to the present time (see the photo below).

The calculating machine of Giovanni Poleni (© Museo Nazionale della Scienza e della Tecnica, Milano)

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

The calculating machine of Giovanni Poleni, 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—so called pin-wheel, invented 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 blocks 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 forth 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 the each one of 3 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 6 dials, i.e. it has 6 digital positions. The tens carry mechanism use a one-tooth wheel and obviously has not been designed well, because it caused problems.

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