284 Dr. Norman Campbell : Experiments on 



state of oscillation through a limited range. This corresponds 

 to the region between 76° 21' and 41° 21', where the curve 

 is below the axis and to the other regions from which this 

 part of the axis is reached after one or more repetitions. 



It will be seen that the highest point of the circle a = 

 resembles an ''essential singularity" of a mathematical 

 function. Within any distance from it, however small, the 

 type of ultimate motion alternates an infinite number of 

 times. 



XXV. Experiments on the High- Tension Magneto. — I. 

 By Norman Campbell, Sc.D* 



Note.— The work described in this paper was carried out 

 at the National Physical Laboratory under the direction of 

 the Advisory Committee for Aeronautics. The results have 

 been communicated in a series of confidential reports to the 

 Internal Combustion Sub-Committee of that Committee, who 

 have now given their consent to the publication of any 

 portions which appear of pure scientific interest. 



I desire to express my obligations to Sir Richard Grlazebrook, 

 Director of the National Physical Laboratory, and more 

 especially to Mr. C. C. Paterson, in whose department the 

 experiments were performed, for invaluable advice and 

 encouragement at all stages of the research. Prof. Taylor 

 Jones was also good enough to discuss very fully the 

 questions which arose in connexion with his theory on which 

 the work is based. 



Object of the Experiments. 

 1. IN the Philosophical Magazine, xxxvi. p. 145 (Aug. 

 A 1918), Prof. E. Taylor Jones has given a theory of 

 the magneto ; this theory is essentially the same as that 

 which he had given previously for the induction-coil, and 

 had shown to predict results in close accordance with ob- 

 servationf. It is not, however, immediately certain that so 

 close an agreement between theory and experiment would 

 be found with the magneto. The theory neglects altogether 

 effects of hysteresis and eddy-currents in the iron core on 

 which the armature is wound, or rather regards these effects 

 as merely adding to the effective resistance of the circuits by 

 which the damping of the oscillations is determined. Since 

 the flux density in the iron is much greater in the magneto 



* Communicated by the Author. 



t See Phil. Mag. xxvii. p. 580 (April 1914). 



