4.1.2 - The resistor

For technical evolution purpose this kind of passive component can be analyzed considering the fixed and variable resitors. The first resistors used in Electronics were known as wire-wound resistor, which generally was made by widing a wire, made of alloys such as the constantanium or nichrome around on an insulating tube. Continuously variable resistors, actually known as potentiometer, considering it was originally used for voltage division by branching a resistor like the volume control on a radio set, basically consists a movable contact along a wire wound resistance or toroid insualting material.
Nowadays the carbon potentiometers are made by applying a carbon film to a horse shoe plate of sinthetic resin bonded paper, along which a slide contact which runs by turning a splindle. Both ends of the horseshoe are silver coated over the carbon layer for the proper connection in the terminals.

Several types of resistors made 1920-1950.
Several types of potentiometer.
In 1827, Dr. George Simon Ohm mathematically demonstrated the relation between resistance, voltage and current in electrical circuits. Ohm's law is fundamental in all resistance calculation. Ohm's researches were published in Germany circa 1827. In 1860 his book was translated to French by J. M. Gaugain with title: Théorie Mathématique des Courants Électriques.
The reproduction of the front pages and author's foreword of the French edition of this landmark in the history of science can be seen in the section Selected Bibliography.