1880J On Effects produced by an Induction Coil, tyc. 



February 19, 1880. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The Right Hon. the Earl of Northbrook was admitted into the 

 Society. 



The following Paper was read : — 



I. u On some of the Effects produced by an Induction Coil with 

 a De Meritens Magneto-Electric Machine." By William 

 SPOTTISWOODE, D.C.L., P.R.S. Received February 17, 1880. 



In the " Philosophical Magazine " for November of last year I gave 

 an account of a mode of exciting an induction coil by the direct appli- 

 cation of one of M. de Meritens' alternating machines, without the 

 intervention of a contact-breaker or the use of a condenser. The 

 experiments of Professor Dewar on the arc furnished by the machine 

 itself, on its spectrum, and on its behaviour in respect of electrolysis 

 described before the Royal Society (see " Proc. Roy. Soc," vol. xxx, 

 p. 170), have led me to think that an account of some of the pecu- 

 liarities in the induced discharge, to which the machine gives rise, 

 might be acceptable to the Society. 



And, first, as regards the secondary discharge in air. It was men- 

 tioned in the paper first quoted that the spark produced by this machine 

 presented an unusually thick yellow flame, and that it was accom- 

 panied by a hissing noise different from that commonly heard with a 

 coil excited by a battery. As the machine gives alternate currents, the 

 secondary discharge presents sparks of equal strength in both direc- 

 tions, and the general appearance to the eye is symmetrical in respect 

 of both terminals. The spark was observed in a revolving mirror, 

 first in a vertical and secondly in a horizontal direction. The discharge, 

 although apparently continuous, was immediately seen to be inter- 

 mittent, with a period in unison with that of the machine. Tongues 

 of flame, leading alternately from one terminal and from the other, 

 crossed the field of view. The length of spark first used (vertically) was 

 about half an inch. When the length was increased to about two inches, 

 the discharge being vertical, flashes or bands of continuous light were 

 seen to traverse the field of view in diagonals of low slope (i.e., nearly 

 horizontally), showing that there were masses of heated matter passing 



