316 THE SO-CALLED SECONDARY ELECTROMOTIVE 



This relation is present in all cases where. there is no disturb- 

 ance from the formation of oppositely polarised regions ; above all, 

 in cases in which the current is led through the schema with one 

 leading-in electrode attached directly to the core. On each side 

 of the remaining single electrode the core is similarly polarised, 

 and this in regularly decreasing degree, so that on each side of the 

 electrode a current is found which, without exception, is directed 

 either from or to it, according as it is an anode or a kathode (taking 

 the direction of the current in the leading-off circuit). I have con- 

 vinced myself by special experiments that it is indifferent with which 

 end of the core the other pole of the polarising current is joined. 

 It is easily conceived that in this simplest ' unipolar ' case the dis- 

 tinction between intra- and extra-polar leading-off, and the descrip- 

 tion of after-currents as -4- and are inadmissible, since both 

 expressions change when the polarising circuit is directly joined first 

 to one then to the other end of the core, without any variations 

 being manifested in the after-currents. 



A second case in which the extrapolar relations appear undisturbed 

 as above, is that in which the combination is only capable of polari- 

 sation on one side, and the extrapolar leading-off is on the side of 

 the polarisable electrode. 



A third case will be mentioned later on. 



These extrapolar conditions, causing currents which, for short, I 

 may be allowed to describe as { idiopolar,' will be disturbed by "the 

 presence in the core of another oppositely polarised region. The 

 two regions seek to equalise their polarisations by currents which 

 run through the fluid from the anodal to the kathodal parts, and 

 which are thus when led-off in character (i.e. directed through 

 the leading-off circuit in opposite manner to the polarising-current) ; 

 these I propose to describe as * bipolar ' currents. Eleven years ago 

 I proved experimentally that these opposed currents were connected 

 with the presence of two oppositely-polarised regions of the core. 



In the intrapolar region, the bipolar current evidently must 

 always be directed similarly to the idiopolar currents which would 

 be shown on either side of the indifference-point in each half of the 

 region. In the intrapolar region, therefore, the after-currents under 

 all circumstances, as well in combinations, polarisable on one side only 

 as in these, must be , and this is borne out by all experiments. 



Much more complicated are $he conditions of the extrapolar 

 regions with doubly polarisable combinations. Here the bipolar- 

 current is opposed to the idiopolar, and the ultimate condition must 



