Найдите в тексте инфинитив и герундий The term "electric current" is used to mean electricity which flows through a conductor, a direct current being a current which flows in one direction only. There are four principal ways by which a direct current can be generated, viz.: 1) chemical action; 2) thermal or heat action, the word thermal, coming from the Greek word "therme" which means "heat"; 3) light action; 4) magnetic action. To set up a current by chemical action, an alkali or an acid is used to react with a metal. Such an apparatus is called an electric cell, a group of two or more cells connected together forming a battery. To produce a current by thermal action, heat is applied to two unlike metals soldered together in two places, the apparatus of this kind being called a thermoelectric couple or thermocouple, for short. We get the prefix "thermo" from "thermal", the origin of the last word having been mentioned above. The word "couple" in this term means that two unlike metals or metals and alloys are joined together so that they can be properly heated in the point of the joint. The reason the thermocouple generates a current is due to the fact that the heat tears the electrons off of the negative metal at the junction, just as the chemical action of an electric cell tears the electrons off of the zinc electrode. It is these electrons that form the current flowing through the circuit. To develop a current by light action, light is made to fall on a special kind of a cell, the apparatus to be used in such a case being called a photoelectric cell. Finally, in order to generate a current, a wire is made to cut, that is, to pass through a magnetic field, this latter being set up either by a permanent magnet or an electromagnet. Where the wire cuts through the magnetic field of a permanentьmagnet, the apparatus is called a magneto-electric machine or just "magneto", for short. The wire cutting through the magnetic field of an electromagnet, the apparatus is called a dynamo electric machine, or "dynamo", for short. In general there are a number of ways by which electric currents can be generated by magnetic action, all of them being based on the same principle, that of cutting the magnetic lines of force with a conductor.

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