I am sufficiently proud of my knowing something to be modest about my not knowing all.

*Vladimir Nabokov*

The mechanical calculating machine of the Jewish clock-maker and jeweler Jewna Jakobson was created around 1770 in the town of Nieswiez on the territory of former Lithuania, then the Russian Empire, Poland, USSR, and now in Belarus. A significant part of the population of Nieswiez was Jewish at that time (middle of the 18^{th} century), with over 700 people. Jews started to settle there in the 16^{th} century, and there was a Jewish community in Nieśwież for more than 200 years until the Holocaust. Polish magnates Radziwill, who owned the Nieswiez Castle from 1533 and ruled the town, granted the Jews certain rights, which made the town a desirable place for them.

Jakobson apparently was a clock-maker and mechanic in the court of Prince Michał Kazimierz Radziwiłł (a Polish–Lithuanian noble and magnate) in Nieswiez. Radziwill family valued culture, arts, and science, and are known for fostering inventors and masters and collecting a significant amount of artifacts and an extraordinary library. In the middle of the 18th century (until 1772, when following the first partition of Polish–Lithuanian Commonwealth, the castle was seized by Russian forces, and the Radziwill family was expelled), these masters created a lot of valuable masterpieces, and obviously one of them was Jewna Jakobson.

Unfortunately, almost nothing is known about the life of Jakobson, and besides the calculating machine, described below, the only historical artifact from him, was a golden chalice, kept until the end of the 19th century in a church in Gnezno village, near Poznan, Poland, which had an inscription, that it has been made by Jewna Jacobson in 1786 (later the chalice has been stolen and it’s lost now). Jakobson probably left Nieswiez at the beginning of the 1770s and moved to Lodz, in Poland.

A calculating machine, created by Jakobson probably sometime around 1770, is now kept in the collection of Lomonosov Museum of Science (Музей имени Ломоносова) in St. Petersburg, Russia (after the seizing of the Nieswiez Castle, the majority of works of art gathered in the palace were distributed among various Russian and Polish nobles in support of Catherine the Great). The device is convenient and reliable for use and has been used for a long time, which can be seen by deep traces of driving keys on the lid of the only preserved copy.

There are three interesting inscriptions on the lid of the machine:

1. *Mechanische Rechnungs Maschine; Machina Mechaniszna do Rachunku*—Mechanical Calculating Machine (in German and Polish).

2. *Zu der Aufgabe des Addirens, Subtantirens, Multiplicirens, und Devidirens von den Nummer Eins bis zu Tausend Millionen und ubrig bleibt von der Division und das kann man hier in der Bruchen zertheilen*—for the purpose of adding, subtraction, multiplication, and division from 1 to 1000 million, the remainder of the division here can be divided to fractions.

3. *Erfunden und verfertigen von dem Hebreer Jewna Jakobson, Uhrmacher und Mechanicis in der Stadt Nieswiez in Lithauen, Gouvernement Minsk*—invented and manufactured by the Hebrew Jewna Jakobson, watchmaker and mechanic in the town of Nieswiez in Lithuania, government Minsk.

Like almost all mechanical calculating devices up until the end of the 19th century, the machine was intended for adding and subtracting. Multiplication and division can be done by means of consecutive adding and subtracting or by using the multiplication table, which is engraved on the lid.

The machine is executed as a compact brass casket with dimensions: 34.2 cm long, 21.8 cm wide, and 3.4 cm high. It has four chiseled legs, 1 cm high and 1,6 cm in diameter each. Jakobson placed pinion groups of neighboring tens on different levels and thus very efficiently utilized the case’s volume. The design of the machine is based on pinion wheels, similar to the wheels of Schickard’s Rechenuhr, although the inventor undoubtedly has not been acquainted with it. There is also an original element—namely a semi-disk (half-disk), which performs the functions of both the input device and the first step in the train of gears.

In the upper part of the machine are mounted nine digital dials, while in the lower part are mounted six digital dials (below a moving lid), which are used for entering the numbers for calculation and for storing intermediate results. Over and below the upper row of nine disks are placed two other rows of semi-disks, which are engaging with the digital disks and are used for entering the digits during adding and subtraction. The numbers are entered by rotating the axes-levers (whose edges are with square sections) of the two rows of semi-disks by means of a special key.

The scale around upper disks consists of digits from 0 to 9, inscribed in the clockwise direction, while the scale around lower disks consists of digits, inscribed in the counterclockwise direction. The result of operations can be seen in the small round windows, which can be seen between the two scales.

On adding operation first must be rotated the axes of the upper row of semi-disks clockwise until the arrow of each semi-disk come to point to the proper digit of the arc-scale. Then the keys are loosed and a special spring returns the semi-disks in starting position, and in the result windows can be seen the first addend. Then in the same manner must be entered the second addend, and the result can be seen in the result windows. The digital disks can be rotated in the starting (zero) position by means of another row of levers, which are below the result windows.

On subtraction, the minuend is entered in the upper row of semi-disks, and the subtrahend is entered in the lower row of semi-disks by rotating counterclockwise. After each entering axes-levers are returned to the starting (zero) position, and the result can be seen in the result windows.

The counting mechanism of each digit position has a semi-disk with nine teeth, whose axis can be rotated by means of the entering key. This semi-disk meshes with the pinion-wheel and rotates it as many teeth, in as many steps is rotated the lever. Over the pinion wheel is fixed the digital disk, and its digits can be seen in the windows. The mechanism for tens carry is a long finger, which once during each revolution engages with the tooth of the next digital position and rotates it to 1/10 revolution.

As we can see, the machine of Jakobson was convenient to handle and a reliable device, and the placement of gears on several levels made it also compact. The smallest details were thought out, up to the marking of parts of the same category with the same sign, so that disassembling and assembling the machine, in case of repair, should be easy, and small recesses in the grooves for the installation keys, which allow precise fixing of the rotary keys in the required position.

A more detailed description of the device can be found in the book: Апокин, Майстров, Развитие вычислительных машин, Москва, Наука, 1974.