T 



706 Prof. E. Taylor Jones and Mr. D. E. Roberts on 



a large reservoir, and observing the quantity of inert gas 

 which had accumulated after a series of suitable intervals of 

 time, it would in all probability be possible to deduce from 

 an examination of the results, not only the final equilibrium 

 amount of helium and neon together, but also the quantities 

 of the two individually, as well as their coefficients of 

 diffusion. 



Palmer Physical Laboratory, 

 Princeton, N.J. 



LXVIII. The Induction- Coil. By E. Taylor Jones, D.Se. 9 

 Professor of Physics in the University College of North 

 Wales, Bangor, and D. E. Eobekts, B.Sc, Fellow of the 

 University of Wales *. 



[Plates XII. & XIII.] 



IHE experiments described in the present paper were 

 made with the object of determining the elements 

 (periods, amplitudes, damping-factors, and phases) of the 

 two electrical oscillations which are set up in the secondary 

 oE an induction-coil when the primary current is interrupted, 

 and of calculating hence the maximum value of the 

 secondary potential and the potential at any time during the 

 oscillations. 



The principal difficulties connected with the calculation 

 of the secondary potential of an induction-coil are (1) the 

 determination of the effective self- and mutual-inductances 

 of the coils, (2) the determination of the capacity of the 

 secondary coil ; the first owing to the want of proportionality 

 between magnetic induction and magnetizing force in the 

 iron core, the second owing to the smallness of the capacity 

 and to the fact that the capacity is distributed along the 

 coil. Some attempt was made in the experiments described 

 below to overcome these difficulties, but there are other 

 circumstances, including condenser losses, hysteresis, and 

 irregularities in the working of the interrupter, which will 

 have to be taken into account, or avoided, before a complete 

 solution of the induction-coil problem can be reached. 



The papers of Oberbeck f, Walter J, and Lord Rayleigh §, 

 on induction-coil potentials are well-known and are therefore 

 only mentioned here. 



* Communicated by the Authors. 



f Oberbeck, Wied. Ann., lxii. p. 109 (1897) ; lxiv. p. 193 (1898). 

 X Walter, Wied. Ann., lxii. p. 300 (1897) ; Ixvi. p. 623 (1898). 

 . § Kavleigh, Phil. Mag-., ii. p. 581 (1901). 



