Eutheeford. — On the Magnetization of Iron. 507 



(2.) Thin steel wire, OOlin. in diameter : Completely de- 

 magnetized. 



(3.) Pianoforte steel-wire, 0-032in. in diameter : Deflection 

 fell from 250 to 116. 



(4.) Steel needle, 0065in. in diameter : Deflection fell from 

 250 to 181. 



(5.) Thick steel needle, 0T02in. in diameter : Fall of deflec- 

 tion from 250 to 216. 



(6.) Hollow soft - iron cylinder, J-mm. thick, diameter 

 18mm., length 16cm. : Fall of deflection, 250 to 230. 



The same condenser and discharging circuit were used for 

 all the specimens tested, and it is of interest to observe the 

 depth of penetration inwards, assuming the residual deflection 

 is given by the mass of iron not circularly magnetized — i.e., 

 not affected by the current in the surface-skin of the con- 

 ductor. 



Experiments of this kind show to what a small depth the 

 current penetrates into the wire. Very large momentary 

 currents are conveyed through a thin surface-skin of the con- 

 ductor, and the intensity of the current diminishes rapidly 

 inwards. 



The loss of deflection due to the " circular magnetization" 

 of a wire by the passage of a longitudinal current is a very con- 

 venient method of estimating the quantities of electricity that 

 flow in the branches of multiple circuits. 



The currents in this case are all of the same frequency, 

 and, experimentally, it was found that the " depth of penetra- 

 tion " was proportional to the maximum current. 



By taking short steel needles magnetized to saturation and 

 placing them in series with circuits in multiple arc, the divi- 

 sion of the current among the conductors admits of accurate 

 determination. By varying the diameter of the needles, 

 currents of the same period but widely different amplitudes 

 may be compared. 



J.J. Thomson has suggested a specially-prepared vacuum- 

 tube placed in a solenoid as. a convenient galvanometer for 

 discharges of this kind. The comparison between the currents 

 in the various branches is made by observations on the bril- 

 liancy of the discharge in the bulb. The effect of a longi- 



