194* Mr. Watkins on Elcctro-mamdic motive Machines, 



Q- 



ing delicately suspended mobile magnets, the shaft and mobile 

 magnets may be made to revolve with considerable velocity. 



Many hundred revolutions in a minute have been assumed 

 as the rate of speed of some of the already constructed re- 

 volving shafts and mobile magnets ; but is it imagined that 

 magnetic attractive force alone actuates the machine so many 

 times within that period, and causes the great velocity? for such 

 a condition of things, I respectfully submit, cannot exist. We 

 certainly have mechanical arrangements which enable us to 

 alter many hundred times in a minute the direction of the 

 inducing electric current about the soft iron ; but the polarity 

 of the soft iron cannot be changed so rapidly if Herschel and 

 Babbage*s law be just, for they say ^Hime is an essential ele^ 

 ment of induction-^" and it is by the induction of the electricity 

 in the wire coils embracing: the soft iron that the magnetism 

 in the soft iron is induced, and thereby an attractive force 

 gained. I am not aware that it has yet been determined what 

 is the exact time necessary for the full development of the in- 

 ductive process, yet experiments tend to prove that it is within 

 the limit of many hundred times in a minute; and as it is ne- 

 cessary for the constant employment of the magnetic attractive 

 force in its full effects that the polarity of each of the opposing 

 poles of the fixed magnets should be in opposite states to the 

 advancing poles of the mobile magnets, it is clear that if the 

 time has not transpired necessary for the transient magnet to 

 acquire its full and proper polarity, there will not be the whole 

 effective magnetic attractive force gained. 



What is it then that aids the rapid revolution of the mobile 

 magnets and carrying shaft when they are light and very free 

 to move, unless it be, their own inertia, when they have 

 acquired a certain velocity, kept up, and contributed to at in- 

 tervals in the revolution by the original prime mover, viz. 

 magnetic attractive force? Now this inertia is a power 

 that is soon overcome by additional friction, as may be 

 observed when a very small portion of weight is added to 

 a shaft which without the additional weight revolves rapidly. 

 The diminution of velocity is immediately perceptible ; and 

 supposing that the slight extra weight thus counteracts the 

 advantage gained by the inertia, then under such circum- 

 stances we have only the primitive magnetic attractive force 

 of the machine left for mechanical purposes. 



I find these conditions maintained in my small models, and 



also in one on a much larger scale which I have made; for on 



augmenting the size of the machine you augment the size of 



the revolving shaft and its magnets ; friction increases conse- 



[* See Pbil, Mag., First Series, vol, Ixvi. p. 98.~Edit.] 



