ST. JOHN — WAVE LENGTHS OF ELECTRICITY. 



223 



With copper wire (diam. 0.027 cm.) five complete oscillations 

 were quite uniformly visible, but with irou wire (diam. 0.027 cm.) 

 only the first return discharge after the pilot spark was faintly 

 visible. 



The time of the double oscillation for the large-sized copper wire 

 was 0.0000020 sec, and for the small copper wire 0.0000021 sec. 

 The author concludes that the magnetic permeability of iron wires 

 exercises an important influence upon the decay of electrical oscilla- 

 tions of high frequency, and 



O O- 



D 



that currents of such frequency 

 as occur in Leyden jar dis- 

 charges magnetize the iron. 

 The data were not sufl&cient 

 to determine whether there was 

 a change of period, but showed 

 that it must be small if such 

 an effect was produced. 



Professor J. J. Thompson 

 has stated that the presence of 

 iron can affect the rapidly 

 oscillating electric discharges 

 through a rarefied gas. His 

 method of showing the phe- 

 nomena is given in Figure 2. 

 C and D are Leyden jars with 

 a spark-gap in the circuit join- 

 ing their inner coatings, and 

 A and B are two loops in the 

 circuit joining their outer coat- 

 ings. In the loop A is placed 

 a bulb exhausted to such a 



degree of sensitiveness that a small change in the electromotive 

 intensity acting upon the bulb produced a considerable effect upon 

 the appearance presented by the discharge. If, when the bulb at A 

 is brilliantly illuminated by the discharge through it, an iron rod be 

 placed in B, the discharge in A ceases ; but if a brass rod is placed 

 in B, the discharge in A is unaffected. 



The author says : " A striking illustration of the difference be- 

 tween iron and other metals is shown when we take an iron rod 

 and place it in B, the discharge in A immediately stops ; if now we 

 slip a brass tube over the iron rod, the discharge in A is at once 



Fig. 2. 



