The simple magneto-dynamo machine, as described above (Fig 90), or electrical generator, as it is now called - to use the modern term; is seen to have a uniform field arranged to be cut by conductors as shown. It will provide an E.M.F. whose magnitude varies sinusoidally, that is the E.M.F polarity and value follows a sine waveform. A sinusoidal waveform is desirable for A.C. working but for the D.C. generator, modifications are necessary to achieve a substantially constant uni-directional voltage magnitude and polarity. It is now apparent that a distinction is being made between the generation of direct current and alternating current and from here on the division between the two methods of generating, transmitting and utilising electrical energy will become marked. In this book, it is hoped that the study of both D.C. and A.C.theory will be given equal attention.