1886.] On the Self-induction of an Electric Current. 



Table L 



457 



Wires, silk -covered, 



1 m. in length, 

 1 mm. in diameter. 



Comparative 

 force of the 

 extra 

 currents. 



Strips or ribbons, silk- 

 covered, 1 m. in length, 

 10 cm. wide, 0*1 mm. 

 thick. 



Comparative 

 force of the 

 extra 

 currents. 



Copper wire, in a single 

 close loop, where each 

 side is in close proxi- 

 mity 



Copper wire, in a single 

 wide circular loop . . . 



Copper wire, in a coil of 

 3 cm. diam., having ten 

 layers in close proxi- 

 mity 



18 

 100 



607 



Copper strip, in a single 

 close loop, where each 

 side is in close proxi- 

 mity 



Copper strip, in a single 

 wide circular loop . . . 



Copper strip, in a coil of 

 3 cm. diam., having ten 

 layers iv close proxi- 

 mity 



14 

 60 



580 



Iron wire (soft), in a 

 single close loop, as 

 above 



Iron wire, in a single 

 circular wide loop . . . 



Iron wire, in a coil as 

 in the case of copper . 



440 

 502 

 570 



Iron strip (soft), in a 



single close loop, as 



above 16 



Iron strip, in a single 



circular wide loop ... 

 Iron strip, in a coil as 



stated for copper .... 578 



There is a remarkable fall in the induction of a straight wire or 

 single wide loop of a copper wire when this wire is doubled upon 

 itself as a return wire in close proximity. The effect of mutual 

 induction is also shown by the equally remarkable rise when the 

 mutual induction of ten layers of a coil react on each other. This is 

 well known, but what I believe has not yet been experimentally 

 observed is the remarkably feeble mutual induction of iron wires, 

 either when in parallel return in close proximity or when in coils of 

 numerous layers. The percentage of increase of induction in a 

 copper wire from a wide single loop to that of the ten layers being 

 507 per cent., whilst in iron under precisely the same conditions there 

 was an increase of but 13 "6 per cent. 



That this remarkable difference as shown between the mutual 

 induction of iron and copper wires is due entirely to the circular 

 magnetism in the iron wire, and that the mutual reactions of the 

 streamlets of the current in a thin flat iron conductor prevent this 

 formation I have proved in various ways, for if the circular magne- 

 tism is the cause, flat iron sheets which have as low self-induction as 

 copper should be equally sensitive to mutual induction as the non- 

 magnetic metals, for they no longer in any appreciable degree possess 

 the protecting magnetic sheath which enfeebles the mutual reactions 

 of iron wires upon each other; this proves to be the case, a thin 



