On Self-regulating Dynamo-electric Machines. 275 



of the horseshoe were very close together, so that there was a 

 small intense magnetic field ; from the juxtaposition of the 

 poles no effect could be produced on a small compass-needle 

 at one tenth of the distance at which I ascertained Wells 

 actually stood — supposing, which is highly improbable, that 

 the lad had the intention to deceive and knew how to attempt it. 

 Numerous questions of interest suggest themselves, such as 

 the photographic and prismatic examination of the luminosity 

 and whether the light is polarized or capable of being pola- 

 rized, or whether the rarefaction and removal of the air around 

 the poles affects the luminosity. The answer to these and 

 cognate questions, together with the examination of some 

 remarkable collateral phenomena that presented themselves 

 — such as the variation of the intensity of the light when 

 viewed in different azimuths, or along or across the magnetic 

 axis, and the effect of certain bodies on the light — will become 

 the subject of investigation by the Committee whenever the 

 testimony to the simple fact itself has been sufficiently well 

 established by various observers. The object of the pre- 

 sent note is merely to demonstrate that there is a strong 

 prima facie case in favour of the existence of some peculiar 

 and unexplained luminosity, resembling phosphorescence, ex 

 cited in the region of the atmosphere immediately around th 

 magnetic poles, and which can only be seen by certain indi- 

 viduals. 



XLI. On Self-Regulating Dynamo-electric Machines. 

 By R. H. M, Bosanquet*. 



DYNAMO-ELECTRIC machines consist mainly of two 

 parts — the armature and the electromagnets ; and the 

 principle associated with the use of the term dynamo is, that 

 the current produced by the armature is, wholly or in part, 

 used to excite the electromagnets. Thus dynamo-electric 

 machines are to be distinguished from magneto-electric 

 machines, in which permanent magnets are used. 



Simple dynamo-electric machines are of two kinds — main- 

 circuit machines and shunt-circuit machines. In main-circuit 

 machines the whole of the main current is sent round the 

 electromagnets ; in shunt-circuit machines a branch current 

 is diverted from the main current, and used to excite the 

 electromagnets. 



Both of these types fail under certain conditions of the 



* Conmiunicated by the Author, being a Paper read "before the Ash- 

 niolean Society, March 5, 1883. 



