﻿440 On Wave-lengths of Electricity on Iron Wires. 



greater than with the iron circuit of the same dimensions, 

 when the spark was constant as far the eye and ear could 

 judge. 



A value can readily he calculated for the damping factor 

 -tu # 

 e m in the case of the iron and copper. Lord Eayleigh's 



formula for the resistance under very rapid oscillations is : — 



R'= VP^R. 



For the iron wire circuit (diameter 0*1186 centim.), Z=1258; 

 /x=430; R=l*67xl0 9 ; p = 36 x 10 7 , whence R' = 403xl0 9 , 

 L = 34xl0 3 . 



The damping factor becomes e— 6xl ° 6 * approximately. 

 The time required for the amplitude to full to one half its 

 maximum value is £ = 000000115 sec. On the basis of 

 115 x 10 6 alternations per second, the number of complete 

 oscillations during this time is 6*5. A like calculation for the 

 corresponding copper circuit gives about 60 times as many. 



The following table shows the results when copper circuits 

 are compared in which wires of different diameters are used: — 



3rd Maximum. 



Copper wire (diameter 0*1201 centim.) 562*5 centim. 



„ „ ( „ 0-0884 „ ) 553-5 „ 



„ „ ( „ 0-07836 „ ) 552-0 „ 



„ „ ( „ 0-03915 „ ) 535-0 „ 



The half wave-lengths calculated from this maximum are : — 

 Copper (0*01201 centim.) 255'8 centim. 

 „ (0-0884 „ ) 252*2 „ 

 „ (0*07836 „ ) 251*6 „ 

 „ (0*03915 „ ) 244*8 „ 

 There are found by dividing the total length of the circuit 

 by 5 :— 



535 X 2 = 1070 length of sides. 



30 ,, closed end. 



124 

 62 x 2= equivalent of end capacities. 



1224-*-5 = 244*8 centim. = half wave-length. 



The range of w r ires suitable for the study of the phenomena 

 is rather limited. If the wires have a greater diameter than 

 1 millim. the difference between iron and copper is slight ; 

 while with w T ires less than 0*5 millim. in diameter the damp- 

 ing is so great that long wires cannot be used, and advantage 

 cannot be taken of the cumulative effect. 



