482 Transactions. — Miscellaneous. 



Dr. Hertz, from his experiments on oscillating circuits, 

 came to the conclusion that iron was not magnetic for very 

 rapid frequencies ; and, to quote from Fleming's abstract of 

 Hertz's researches (vol. i., p. 416), "Hertz supposed that, as the 

 self-inductance of iron wires is for slow alternations from eight 

 to ten times that of copper wires, therefore a short iron wire 

 would balance a long copper one ; but this w T as not found 

 to be the case, and he concludes that, owing to the great 

 rapidity of the alternations, the magnetism of the iron is 

 unable to follow them, and therefore has no effect on the 

 self-induction." And again, p. 423: "When the wire was 

 surrounded by an iron tube, or when it was replaced by an 

 iron wire, no perceptible effect was obtained, confirming the 

 conclusion previously arrived at that the magnetism of the 

 iron is unable to follow such rapid oscillations, and therefore 

 exerts no appreciable effect." 



Steefan has, however, shown that we could expect very 

 little alteration in the inductance of a wire, even if it were 

 magnetic, en account of the greater concentration of the 

 current in a magnetic conductor on the surface of the 

 wire. 



Professor J. J. Thomson (" Recent Researches," p. 322, 

 and " Philosophical Magazine," 1891, p. 457) has shown that 

 an iron cylinder placed in a solenoid absorbs considerably 

 more energy than a similar non-magnetic conductor of equal 

 conductivity, on account of the higher permeability of the 

 iron. 



J. Trowbridge (" Damping of Electric Oscillations " : Phil. 

 Mag., December, 1891) has shown that the resistance of iron 

 wires damps electrical energy very considerably, and has 

 deduced that iron must have a fairly high permeability to 

 account for the effects observed. 



Lastly, we have the statement, in the last page of Gray's 

 " Absolute Measurements," that the damping of oscillations in 

 a resonator is greater when the wire is of iron than when it is 

 of copper. 



In order to investigate the effect of " magnetic penetra- 

 tion " in iron for fields varying very much more rapidly than 

 could be obtained with the use of the " time apparatus," the 

 readiest means to hand for obtaining a very rapid oscillatory 

 current was the ordinary ley den- jar discharge. 



The subject of the magnetization of iron in these fields has 

 been very little touched upon since the time that Henry 

 experimented on the effect of leyden-jar discharges on the 

 magnetization of steel needles. 



In the experiments that follow it will be shown that iron 

 is strongly magnetic in rapidly-varying fields, even when the 

 frequency is over 100,000,000 per second. 



