Reochord

A reohord (Voltagometer) is a rheostat that makes it possible to measure electrical resistance using the Wheatstone bridge method and determine the electromotive forces in galvanic cells using the compensation method . Reohord is a homogeneous conductor in the form of metal wire or string with a movable contact and a graduated scale. By moving the contact along the string, it is possible to achieve a change in the magnitude of the current or voltage in the circuit.

The first reohord was built by the German physicist Johann Poggendorf in 1841. It was a straight calibrated wire about a meter long, on which the contact was formed, forming two arms. Against each point of a reochord, the ratio of his shoulders was noted on the ruler.

A few years later, Academician Boris Jacobi constructed a similar device, which he called a voltagometer. Unlike the Poggendorf reichord, Jacobi's voltagometer consists of a drum and a calibrated wire wound around it. Rotating the drum, you can include in the chain any part of the resistance, which in this case can be counted on a scale. In the practice of measuring, Jacobi then perfected the voltagometer. Noticing that the resistance of contact between the rolling wheel and the wire is not consistent, he arranges mercury contacts in the voltameter. And later goes on to the design of a mercury voltagometer, in which the resistance is mercury.