Magnetic Induction in Iron and other Metals. 337 



Let there be drawn firmly on a piece of tracing-paper 

 a curve like that of fig. 4, P, which represents approximately 

 the resultant of two simple harmonic motions of equal ampli- 

 tudes, and with periods as 1:2. 



Fig. 4, P. 



Now let the tracing-paper be folded over on itself until the 

 point B coincides with A, and there will be seen through the 

 tracing-paper the curve shown in fig. 4, Q. This last is a 



Fig. 4, Q. 



familiar type of curve in connexion with the effects of stress 

 on the magnetic and thermoelectric properties of some 

 materials. 



Conversely, any closed curve which, like fig. 4, Q, repre- 

 sents the effect of a cyclic change in the independent variable, 

 may be supposed to be opened out into the form of an open 

 curve like fig. 4, P. 



