DIRECT CURRENT MACHINES.

The genesis of the ideas required to build an electrical machine can be traced back to the discovery of electromagnetism by the Danish scientist Oersted in 1819-20. Oersted discovered that a current in a wire could deflect a compass needle. Thus the connection between a current carrying conductor, a magnetic field and mechanical movement was established. A German chemist named Schweigger, who studied Oersted's experiment, found that if the wire carrying the current was wound into a coil then the deflection of the magnet was greatly increased. The Professor of Chemistry at Cambridge, Cumming, coined the term ‘Galvanometer' for this configuration and used it as a current detector. At around the same time Ampère developed a theory to support the observations made about current carrying coils of wire. In 1825 Sturgeon found that putting an iron core in the coil increased the magnetic field strength considerably for the same current. [ABSTRACT FROM AUTHOR]