The three most important effects of the current just mentioned, may be presented in more detail as follows: 1. The _Thermal effect:_-- The conductor along which the current flows becomes heated. The rise of temperature may be small or great according to circumstances, but some heat is always produced. 2. The _Magnetic effect;_ The space both outside and inside the substance of the conductor, but more especially the former, becomes a “magnetic field” in which delicately pivoted or suspended magnetic needles will take up definite positions and magnetic materials will become magnetized. [Illustration: FIG. 87.--Lenz’s apparatus for measuring the heat given off by an electric current. It consisted of a wide mouthed stoppered bottle fixed upside down, with its stopper, _b_ in a wooden box; the stopper was perforated so as to give passage to two thick platinum wires, connected at one end with binding screws, _s_, while their free ends were provided with platinum cones by which the wires under investigation could be readily affixed; the vessel contained alcohol, the temperature of which was indicated by a thermometer fitted in a cork inserted in a hole made in the bottom of the vessel. The current is passed through the platinum wires, and its strength measured by means of a galvanometer interposed in the circuit. By observing the increase of temperature in the thermometer in a given time and knowing the weight of the alcohol, the mass of the wire, the specific heat, and the calorimetric values of the vessel, and of the thermometer, compared with alcohol, the heating effect which is produced by the current in a given time can be calculated.] 3. The _Chemical effect;_-- If the conductor be a liquid which is a chemical compound of a certain class called _electrolytes_, the liquid will be decomposed at the places where the current enters and leaves it. =Thermal Effect.=--If a quantity of electricity were set flowing in a closed circuit and the latter offered no _resistance_, it would flow forever, just as a wagon set rolling along a circular railway would never stop if there were no _friction_.