History of electric light

During the first few years after 1840 the dynamo was only a laboratory experiment. Woolrich devised a machine which had several pairs of magnets and double the number of coils in order to make the current obtained less pulsating. Wheatstone in 1845 patented the use of electro-magnets in place of permanent magnets. Brett in 1848 suggested that the current, generated in the coils, be allowed to flow through a coil surrounding each permanent magnet to further strengthen the magnets. Pulvermacher in 1849 proposed the use of thin plates of iron for the bobbins, to reduce the eddy currents generated in the iron. Sinsteden in 1851 suggested that the current from a permanent magnet machine be used to excite the field coils of an electro-magnet machine.

In 1855 Soren Hjorth, of Copenhagen, Denmark, patented a dynamo having both permanent and electro-magnets, the latter being excited by currents first induced in the bobbins by the permanent magnets. In 1856 Dr. Werner Siemens invented the shuttle wound armature. This consisted of a single coil of wire wound lengthwise and counter sunk in a long cylindrical piece of iron. This revolved between the magnet poles which were shaped to fit the cylindrical armature.