The disk dynamo

The disk dynamo consists of a rotating disk connected by brushes to a coil coaxial with the disk. If a couple is applied to the disk the dynamo can generate current. If it is provided with a shunt across the coil and with a series impedance it gives a current which reverses in an apparently random manner. A pair of interconnected dynamos, without shunts shows similar reversals. The disk dynamo is a system with 3 degrees of freedom, it is the simplest known example of pseudo-stochastic behavior in a mechanical system. The paper describes the development of this behavior as the couple, the shunt and the series impedance are successively added to the machine. The resemblance of the behavior of a disk dynamo to that of a dynamo in a sphere of conducting fluid is discussed. The reversals are compared to those of the earth's magnetic field.