NO. 2 



HISTORY OF ELECTRIC LIGHT- 



l 



-SCHROfeDEk 



27 



FURTHER DYNAMO DEVELOPMENTS 



In the summer of 1886 Sir Charles Wheatstone constructed a self- 

 excited machine on the principle of using the residual magnetism in 

 the field poles to set up a feeble current in the armature which, 

 passing through the field coils, gradually strengthened the fields until 

 they built up to normal strength. It was later found that this idea 

 had been thought of by an unknown man, being disclosed by a clause 

 in a provisional 1858 English patent taken out by his agent. Wheat- 

 stone's machine was shown to the Royal Society in London and a 



Wheatstone's Self-Excited Dynamo, 1866. 



This machine was the first self-excited dynamo by use of the residual 

 magnetism in the field poles. 



paper on it read before the Society on February 14, 1867. The field 

 coils were shimt wound. 



Dr. Werner Siemens also made a self-excited machine, having 

 series fields, a paper on which was read before the Academy of 

 Sciences in Berlin on January 17, 1867. This paper was forwarded 

 to the Royal Society in London and presented at the same meeting 

 at which Wheatstone's dynamo was described. Wheatstone probably 

 preceded Siemens in this re-discovery of the principle of self-excita- 

 tion, but both are given the merit of it. However, S. A. Varley on 

 December 24, 1866, obtained a provisional English patent on this, 

 which was not published until July, 1867. 



In 1870 Grarrime, a Frenchman, patented his well-known ring 

 armature. The idea had been previously thought of by Elias, a 



