246 Mr. Albert Griffiths : Some 



There are some surmises with regard to the action of a rise 

 of temperature. 



Addendum I. contains a thorough discussion of the be- 

 haviour of the method of differential winding for diminishing 

 the spark on breaking a galvanic circuit. 



Addendum II. gives a theoretical treatment of the working 

 of the interrupter which may be useful when it is necessary 

 to design an interrupter for high frequencies. 



Addendum III. describes the method adopted to compare 

 self-inductions. 



In conclusion I have to express my thanks to Prof. A. 

 Schuster for initiating my research and for much friendly 

 criticism throughout. 



Addendum I. 



In the method of differential winding two wires of equal 

 length and diameter are wound into coils side by side, and 

 their ends so connected that the wires are in parallel arc and 

 that the equal currents which circulate the coils, when a steady 

 current is flowing, go in opposite directions. When a steady 

 current goes through the arrangement no lines of force are 

 produced within the combination coil ; one naturally associates 

 the production of a spark at a break in a coil with lines of 

 force, and there is a danger of erroneously assuming that no 

 spark due to induction will be formed by causing a break in 

 one of the coils. What is, of course, necessary, is that the 

 rate of change of the number of lines of force enclosed within 

 the coil should equal zero. 



Let us imagine that one coil can be suddenly broken at any 

 point, and that the current in the other coil can flow on 

 undisturbed : if this happened the lines of force enclosed 

 within the combination coil would instantaneously vary from 

 zero to a finite number, i. e. } the rate of change of the number 

 of lines of force would equal infinity and the E.M.F. tending 

 to produce a spark across the gap would also equal infinity. 



What actually happens is, probably, somewhat as follows : 

 since the self-induction of each coil is equal to the mutual 

 induction of the two, on breaking one coil the current in the 

 other is suddenly stopped, it then begins immediately to 

 increase, and whilst increasing causes, by induction, a spark 

 across the gap in the broken coil. 



The spark produced by the break is therefore analogous to 

 the " make " spark of an ordinary induction-coil. 



The stoppage of both currents by the break of only one 



