Basic device

Initially, wooden planks (wands) were used to measure the bases, but since the tree varies greatly with temperature and humidity, such a measurement was extremely inaccurate. Over time, wooden wands were replaced by metal ones, and various devices were arranged for determining the length and for sequential stacking of the wands. The scientist Borda was the first to make wands from two dissimilar metal strips. His device consisted of 4 wands; each rod was composed of platinum and copper strips fastened at only one end. The difference in the lengths of these two bands at different temperatures was measured by the nonius , and this directly determined the temperature . Thus, each wand of the Bord device was a metal thermometer . The Borda basic device has been used in France since the time of Great Fr. revolution; The idea of ​​this scientist was also used by many later inventors of basic devices.

In the 19th century, basic devices began to be arranged in a very diverse manner; each almost European state had a special system device. The best and most practical devices, both in terms of the simplicity of the device and the satisfactory accuracy of the results obtained, at that time were the basic devices of V. Struve and Bessel. B. Struve Ave., used in the Russian Empire, consisted of 4 wands, each of them 2 toaz long. The temperature of each wand is measured by 2 mercury thermometers, of which the balls are in the recesses drilled in the wands. The wands were equipped at the ends with special devices that make it possible to touch two adjacent wands without the slightest blow. This device was used to measure all the most important bases in Russia at the end of the 19th and beginning of the 20th centuries. A detailed description of it was placed in the work of V. Struve: "The arc of the meridian between the Danube and the Arctic Sea." The basic device of Bessel, adopted in Prussia and arranged according to the idea of ​​Reichenbach, consists of 4 wands, each with a length of 2 toilets. Each rod consists of two strips, iron and zinc, with different expansion coefficients, and ends with steel wedge-shaped points. To measure a small gap between the endpoints of adjacent wands, as well as to measure the difference in length between the two strips, a special glass wedge was inserted, polished at a very sharp angle. In addition to these devices, there are many others even more accurate, such as, for example, the Spanish basic device and the English compensation device. These instruments are equipped to observe the accuracy of the sequential installation of wands by microscopes , which were first used by the American Gassler . Struve and Bessel instruments gave accuracy up to 1/60000 of the basis value, they were measured quite quickly: up to 200 wands can be laid in one day. The Spanish and English instruments gave greater accuracy , but their measurement of the basis, if necessary, was extremely slow.

A typical modern basic device consists of Invar wires having a scale marking at the ends. These scales measure the distances between the “pillars” that are mounted on tripods at distances of 24 m from one another. The pillars are cylindrical in shape; two mutually perpendicular strokes are applied to their convex upper bases. The wire is then pulled using blocks with two 10 kg weights . At the same time, its scales are brought to the strokes of the pillars, after which readings up to 0.1 mm are made on the eye. The length of a straight line connecting the corresponding strokes of the scale of a wire stretched by kettlebells is the subject of measurement. Using a 3-meter Invar rod, the length of this line is measured by a special measuring device, which was called the comparator ^[1] .

• Basic device // Brockhaus and Efron Encyclopedic Dictionary : in 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.