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LXV. Induction- Coil Potentials. By E. Taylor Jones, 

 D.Sc, Professor of Physics in the University College o, 

 J^orth Wales, Bangor *. 



[Plate VIII.] 



THE present paper contains some further applications of: 

 the theory of electrical oscillations in coupled circuits, 

 and is a continuation of two former papers f on fche subject. 

 In the first of these it was shown that if a given current 

 is interrupted in the primary of two coupled oscillatory 

 circuits, the potential-difference, V 2 , at the terminals of the 

 secondary at any subsequent time t is theoretically given by 

 an expression of the form 



Ax*-** sin (2*71!* — 8,) — A a *-** sin (27rn 2 ^S 2 ), . . (1) 



where w l5 n 2 are the frequencies of the two oscillations of the 

 system, and the other six constants can be calculated from 

 the capacities, inductances, and resistances of the circuits. 

 This result was illustrated by a number of examples in which 

 coupled air-core coils connected to condensers were used. 

 The wave of potential represented by (1) was worked out for 

 each case and compared with the experimental curve obtained 

 with an electrostatic oscillograph. 



In the second paper referred to, the expression (1) was 

 further illustrated by experiments with an ordinary induc- 

 tion-coil with iron core, a number of cases being worked out 

 in some of which the secondary coil, as well as the primary, 

 was connected to a condenser. In these experiments, how- 

 ever, the primary (paraffin-paper) condenser was of con- 

 siderably greater capacity than that generally used with an 

 induction-coil. 



Recently an expression of the form (1) has been given in 

 an important paper by Dibbern J for the potential-difference 

 at the plates of the primary condenser, and the theoretical 

 curves of both primary and secondary potential compared 

 with the experimental curves obtained with a pendulum 

 interruptor. In his experiments Dibbern used coils with 

 air-cores, cores of iron-filings in paraffin-wax, of iron wire, 

 and of solid iron. Good agreement was found between the 



* Communicated by the Author. 



t " Electrical Oscillations in Coupled Circuits," E. T. Jones, Phil. Mag. 

 xvii. p. 28 (1909) ; " The Induction-Coil," E. T. Jones and.D. E. Roberts, 

 Phil. Mag. xxii. p. 706 (1911). These two papers will be referred to as 

 I c. (1) and I. c. (2). 



+ E. Dibbern, Ann. d. Physik, xl. 4, p. 935 (1913) : Inaug-.-Diss., 

 Kiel. 



