Direct Currents

Direct Currents of electricity are those in which the electric displacements along the conductor take place continuously in the same direction. In this respect they differ from alternating currents, where the displacements are continually oscillating backwards and forwards. As for the advantages of either system in electrical engineering, no one is at present really qualified to give an ultimate answer. Whereas direct currents are simpler to work, their instruments easier to design and understand, and their behaviour in novel combinations readily to be predicted, alternating currents, on the other hand, offer serious difficulties in each of these respects. But so little is known of alternating currents as yet that it is useless to condemn them on account of the above difficulties. Alternate current generators are certainly better in some ways [Dynamo], and transmission of power by means of such currents is already the more convenient. Moreover, the recent researches of Hertz, Tesla, and others point to an immense extension of the principle of power transmission in an alternating system, and a fuller knowledge of this is hoped for and expected by many. Both direct and alternating currents may be used for the electric light, which depends for its production on the generation of a white heat in an imperfect conductor that offers considerable resistance to the motion of electricity. Inasmuch as such a conductor offers resistance to motion in either direction, its heating is continuous though the current be alternating. In electro-metallurgy, where currents are made to deposit metals from solution, a reversal of the current produces a reversal of the deposition. Alternating currents are in that case useless, direct currents alone being employed.