256 J. A. POLLOCK. 



similar dimensions were employed in verifying the results, 

 and it was definitely proved that the measurements were 

 wholly independent of any characteristic of the receiving 

 circuits. 



In his theoretical discussion of this subject Abraham 1 

 considers the vibration about a perfect conductor in the 

 form of an elongated ellipsoid of revolution. When the 

 minor axis (2b) becomes negligibly small in comparison witli 

 the major axis (I), the wave-length in free ether of the 

 disturbance due to the fundamental vibration is equal to 21. 

 In a second approximation Abraham obtains the following 

 expression for this wave-length: — 



A = 21 (1 + 5*6€ 2 ) 

 where 1/c == 4 log e l/b. , 



In the table, under the heading c A. calculated,' are given 

 the wave-lengths deduced from this equation, and under 4 fc 

 calculated,' the ratio of these wave-lengths to the lengths 

 of the oscillators. 



A consideration of the evidence shows that Abraham's 

 expression gives a result for the wave-length which agrees 

 with the measured value within the present limits of 

 experimental error. This was Ives' conclusion in 1910, 

 and the results now published add to his statement but the 

 weight attached to confirmation from independent work. 

 The physical accuracy of Abraham's deduction is now 

 sufficiently well established for linear oscillators of known 

 dimensions to be used as standards in connection with the 

 measurement of short electric waves. 



These results completely support Lord Rayleigh's 2 view 

 of the value of the wave-length of the vibration on a thin 

 straight terminated rod, and at least imply the experi- 

 mental verification of his contention " that the difference 



1 Abraham, loc. cit. 2 Eayleigh, loc. cit. 



