970 Mr. M. Siegbalm on the Study of Variable 



cases one variable may be expressed as the function of the 



° ther ' ' -/© (2) 



For a long time we have used the graphic representation 

 for the magnetic magnitudes, and thus learnt to master them. 

 Also in a closely connected branch of electricity, i. e. the 

 electric machines, the graphic method has been used to 

 advantage. This has particularly been the case, since 

 Hopkinson's epoch-making works made it possible for us to 

 calculate " magnetic loops." For alternate currents this 

 excellent method has only recently begun to be made use of. 

 It was not until Kauffmann * had proved its applicability to 

 electricity passing through gases, and developed the conditions 

 of stability, that it could come into proper use where alternate 

 currents are concerned. 



I. Characteristics. 



If the function (2) is graphically represented, the so-called 

 cluiracteristic curve is obtained. We will now consider the 

 most important qualities of these curves. 



Fig. 1 reproduces a characteristic curve or, more shortly, 



Fig. 1. 



a characteristic. It gives for any z-value the corresponding 

 value of e, supposing i. e. one has in every point to deal with 

 a stationary state. To exemplify our case we may take 



♦ W. Kauffmann, Ann, d. Physik (4) ii. p. 158 (1900). 



