276 Mr. R. H. M. Bosanquet on Self-regulating 



external resistance ; and the conditions of failure are opposite 

 in the two cases. 



Main- circuit machines fail when the external resistance is 

 high ; for then the current produced is small, the excitation 

 of the magnets fails, and the action ceases. 



Shunt-circuit machines fail when the external resistance is 

 low, as when the carbons of an arc lamp accidentally touch, 

 and the resistance becomes very small ; for then the whole 

 current is diverted from the shunt to flow through the short 

 circuit, the excitation of the shunt magnets fails, and the 

 action ceases. 



It has been proposed by several persons, independently, to 

 get rid of these failures by combining the two modes of ex- 

 citation. For this purpose the magnets are wound both with 

 main and shunt coils — the main coils carrying the main circuit, 

 and the shunt coils carrying a derived circuit. The main 

 coils are most strongly excited when the shunt coils fail ; and 

 the shunt coils are most strongly excited when the main coils 

 fail. Machines wound with both main and shunt coils have 

 been called compound machines, as opposed to the original 

 simple types with main coils only or shunt coils only. 



Compound machines are capable of being arranged so as 

 to fulfil certain conditions — for example, to give a constant 

 E.M.F. for varying values of the external resistance. When 

 arranged to satisfy any such requirement, they have been 

 called self-regulating machines. 



Several types of self-regulating machines are in the market ; 

 but their principles have not been made public. 



The first publication on the theory of this matter appears 

 to have been by Marcel Desprez, in l La Lumiere electrique ;' 

 this publication is not accessible here. From the accounts 

 that have been given of it, it does not appear to treat the 

 matter from my point of view. 



The first publication on the theory in England, so far as I 

 know, was in a letter I wrote to the ' Electrician ' in December 

 1882, in which I gave the deduction of the form of compound 

 machines to produce constant E.M.F. at constant velocity, 

 based on the simplest theoretical assumptions. 



This letter produced numerous communications from in- 

 ventors claiming the priority in such machines — more especially 

 a general description by Mr. Paget Higgs, and a series of 

 papers by Mr. Gisbert Kapp, in one of which a graphical 

 method was described for the examination by trial of different 

 forms of winding, no doubt a satisfactory means of arriving 

 at practical results. Attention has also been called to the 

 matter in various public lectures. These have been partly 



