Electric Waves along Wires. 665 



the final position being determined only by the results of 

 observations taken when the sparking was in one of its most 

 regular states. 



An approximate result was obtained in a few minutes, but 

 frequently the observations continued for several days before 

 the sparking was sufficiently reliable to aive results on which 

 to base the final adjustments. Not till the position of the 

 bridge was finally settled were the measurements of the 

 circuit made, so that these are here given as exactly as it was 

 possible to take them, with the bridge in the definite position 

 previously decided upon, though this position was not deter- 

 minable with the accuracy with which the measurements were 

 taken. 



The possible error in the result given for the stoutest copper 

 fdiam. '076 cm.) does not exceed about *05 per cent. 



After each of the wires had in turn formed the secondary, 

 a second determination was made with the *076 cm. copper, 

 and when the measurements were taken the length was found 

 to be 1299'05 cm., differing by *1 cm. from the previous 

 result. 



No pretence is made to this degree of accuracy; in fact it 

 was found later that small irregularities in the wire (such as 

 probably were present in the first instance) increased the 

 length to 1299*35 cms. This is, however, sufficient to show 

 the reliability of the results. The average of the two readings 

 is given in the table. With the finer wires the maxima were 

 not so well marked because of the greater damping, and the 

 determinations were not so accurate, the possible error for 

 the finest copper wire amounting to about *2 per cent. 



To demonstrate the dependence of the velocity on the wave- 

 length, the same wires were used in the secondary when the 

 primary had a frequency almost twice that in the previous 

 series. The results are tabulated on p. 66Q, and show the dimi- 

 nution of velocity in the finer wires to be greater with the 

 higher frequency. 



The difference in the wave-lengths measured along wires 

 of different diameters, the parallel wires being 7*8 cm. apart, 

 is considerably greater than that calculated as by Sommerfeld 

 for isolated wires. 



Fig. 5 shows the relation between the velocity along copper 

 wires and the diameter of the wires (the parallel wires in this 

 experiment being 7*8 cm. apart). The curves were obtained 

 by plotting the variations from the velocity along '076 cm. 

 copper wire as ordinates and the diameters of the wires as 

 abscissa?, the wave-lengths along *076 cm. wire being 



Phil. Mag. S. 6. Vol. 1. No. 6. June 1901. 2 X 



