In a magneto-electric machine the commutator revolves identically with the magnet or armature, and the point at which sparks are being constantly produced is where the contact is being continually broken and made by the passage of the friction springs from over the non-conducting layer. The first machine formed on the basis of Faraday’s experiments was Pixii’s. It was composed of two uprights and a cross bar, to which is attached, hanging poles downwards, an electro-magnet; underneath this, the poles upwards, revolves a magnet. The commutator is fixed on the same axle and revolves with the permanent magnet. Saxton, and subsequently Clarke, made the obvious improvement of making the magnet less cumbrous and fixed, and causing the bobbins of the electro-magnet to revolve before or rather beside its poles; the commutator was fixed at the end of the axle on which the revolving bobbins (or armature) are fixed. Niaudat formed a compound Clarke machine, by setting two horse-shoe magnets a short distance apart. The armature revolves between them, and consists of twelve coils set between two plates; the coils are set alternately and connected,—_i.e._, the poles of the electro-magnets are set beside one another,—N. to S., S. to N., and so on, so that the N. pole receding produces a current; _but_ the N. pole receding makes the S. pole approach, and produces another current, A B; in fact, a continuation of the same, for the _approach_ of a N. pole naturally produces the same current as the recession of a S. pole; then as the S. pole in turn recedes it produces an inverse current, B A, which is in turn kept up by the approach of the next N. pole, and so on. Each coil is attached to a radiating metal bar, which conveys the current to be redirected to the commutator, which is affixed to the axle of the revolving armature as in Clarke’s machine. In 1854 Siemens completed his machine, the chief peculiarity of which was its cylindrical bobbin; the core is grooved deeply, parallel with its axis, and the wire is wound on cylindrically and covered with plates of brass; one end of the coil is fixed to the metal axis, the other to an insulated ferule at the end of the axis, where is also situate the commutator. This armature revolves between the poles by which it is closely embraced. One of the most celebrated of the magneto-electrical machines is that known as the “Alliance,” invented by Nollet, and perfected by Van Malderen. It is composed of four or six bronze discs, revolving on an axle, round the external circumference of each of which are set sixteen bobbins. This rotating compound armature revolves between four to six sets of horse-shoe magnets, which, being fixed radially to the centre, present in each set sixteen poles to the sixteen bobbins. It will be readily understood that this immense quantity of poles and bobbins produces a highly concentrated current, the ends of which proceed from the axle and an insulated ferule at its extremity.