494 Transactions. — Miscellaneous. 



condenser, as in Lodge's experiment on the velocity of electric 

 radiation. 



Plate XLIX., Fig. 9. 



BD, TF, were a pair of wires, each about 20 yards long, 

 leading from the condenser. This length was timed as far as 

 possible to be in unison with the discharge at A : i.e., the 

 length of one of the wires was half a wave-length. With ^in. 

 spark at A, a spark of fin. could be obtained at spark-gap D, 

 and the ends gave off a beautiful glow discharge every time a 

 spark occurred at A. 



The deflection of the needle always fell in value after a dis- 

 charge, and there was not such a difference between the 

 amplitude of the first and the second balf-oscillation as in the 

 previous cases. 



With discharge in one direction deflection fell from 310 

 to 250 ; with discharge in opposite direction deflection fell from 

 300 to 255 : showing that the first and second half-oscillations 

 do not differ much in amplitude. 



It seems very probable that when the long wires are 

 timed in unison with the discharging current the rate of 

 decay of vibrations in the long wires is independent of that of 

 the discharging circuit. The long wires act as a resonator, 

 and oscillate long after the oscillations in the vibrator have 

 ceased. It made very little difference in the effect on the 

 needle whether the knobs at the ends of the long wires were 

 close together or far apart. To magnetize iron in rapid fields 

 a closed circuit is not required. Another example of this will 

 be given later. 



From this and the previous experiment we see that iron 

 is magnetic under the influence of impulsive rushes of elec- 

 tricity. 



III. Effect of Induced Secondary Currents on the 

 Magnetization of Iron. 



Plate XLIX., Fig. 10. 



A primary coil of ten turns of insulated wire was placed 

 inside a glass tube, and a secondary of twelve turns outside 

 the tube. A discharge was passed through the primary, and 

 induced currents obtained in the secondary, giving a small 

 spark at B. When a magnetized steel needle 0-032 in diameter 

 was placed in a solenoid of three turns to the centimetre the 

 deflection fell from 300 to 261. 



In order to see the effect of resistance on the amount of 

 current in the secondary, 10 yards of platinoid wire was placed 

 in series with the secondary. Deflection fell from 300 to 285. 



On removing platinoid wire and placing a copper wire of 

 same length and section in its place very little difference in 



