"The discovery of induction by Faraday, in 1831, gave rise to the construction of magneto-electro machines. The first of such machines that was ever made was probably a machine that never came into practical use, the description of which was given in a letter, signed 'P. M.,' and directed to Faraday, published in the Philosophical Magazine of 2nd August, 1832. We learn from this description that the essential parts of this machine were six horse-shoe magnets attached to a disc, which rotated in front of six coils of wire wound on bobbins." Sept. 3rd, 1832, Pixii constructed a machine in which a single horse-shoe magnet was made to rotate before two soft iron cores, wound with wire. In this machine he introduced the commutator, an essential element in all modern continuous current machines. "Almost at the same time, Ritchie, Saxton, and Clarke constructed similar machines. Clarke's is the best known, and is still popular in the small and portable 'medical' machines so commonly sold. ... A larger machine [was] constructed by Stöhrer (1843), on the same plan as Clarke's, but with six coils instead of two, and three compound magnets instead of one. ... The machines, constructed by Nollet (1849) and Shepard (1856) had still more magnets and coils. Shepard's machine was modified by Van Malderen, and was called the Alliance machine. ... Dr. Werner Siemens, while considering how the inducing effect of the magnet can be most thoroughly utilised, and how to arrange the coils in the most efficient manner for this purpose, was led in 1857 to devise the cylindrical armature. ... Sinsteden in 1851 pointed out that the current of the generator may itself be utilised to excite the magnetism of the field magnets. ... Wilde [in 1863] carried out this suggestion by using a small steel permanent magnet and larger electro magnets. ... The next great improvement of these machines arose from the discovery of what may be called the dynamo-electric principle. This principle may be stated as follows:--For the generation of currents by magneto-electric induction it is not necessary that the machine should be furnished with permanent magnets; the residual or temporary magnetism of soft iron quickly rotating is sufficient for the purpose. ... In 1867 the principle was clearly enunciated and used simultaneously, but independently, by Siemens and by Wheatstone. ... It was in February, 1867, that Dr. C. W. Siemens' classical paper on the conversion of dynamical into electrical energy without the aid of permanent magnetism was read before the Royal Society. Strangely enough, the discovery of the same principle was enunciated at the same meeting of the Society by Sir Charles Wheatstone. ... The starting-point of a great improvement in dynamo-electric machines, was the discovery by Pacinotti of the ring armature ... in 1860. ...