Absorption of Electric Waves along Wires. 39 



or of electric currents producing the magnetic field in which 

 the needle is placed, since the equation d$/dx=dF jdy holds 

 in all cases. 



I hope that in what precedes I have correctly understood 

 Professor Holman's notation. His m, defined by him to be 

 " the strength of pole of any thin transverse section or shell 

 of the needle/'' I take to be that quantity which multiplied 

 by the thickness ds of the shell gives mds as the magnetic 

 moment of the shell ; in other words it is, as stated above, the 

 magnetic moment per unit length of the bar. It seems 

 necessary to make this remark, as Messrs. Ayrton and Mather, 

 in their reply, interpret Professor Holman's m differently, 

 namely, as the amount of free magnetism per unit length at a 

 given cross-section of the bar. In this sense m is zero every- 

 where except at the ends, where it is infinite, inasmuch as 

 according to the theory of magnetic matter the finite, equal, 

 and opposite quantities of magnetism are surface distributions 

 on the end-faces. 



Bangor, November 1896. 



"VII. Absorption of Electric Waves along Wires by a Terminal 

 Bridge. By Edwin H. Barton, B.Sc, F.R.S.E., Senior 

 Lecturer in Physics at University College, Nottingham, and 

 Geo. B. Bryan, B.Sc, " 1851 Exhibition " Research 

 Scholar*. 



IN the discussion on Mr. Yule's electrical paper last yearf, 

 one of us stated his intention of endeavouring to realise 

 experimentally the extinction of electric waves along wires 

 on their arrival at the end of the line, the urgent desirability 

 of this having been felt by several investigators J. The question 

 is probably of interest also in connexion with Telephony. 

 This task, small as it may seem, we had no opportunity to 

 attack till this summer. The adoption of a resistance-bridge 

 for the absorption of the electric waves was originally sug- 

 gested by Mr. Oliver Heaviside's mathematical proof § that, 

 given a bridge of suitable resistance at the end of a line, then 

 the waves arriving there would be immediately absorbed ; 



* Communicated by the Physical Society: read November 13, 1896. 



t Gr. U. Yule, " On the Passage of an Oscillator Wave-Train through 

 a Plate of Conducting Dielectric," Proc. Phys. Soc. vol. xiii. pp. 358-392 

 (1895) ; Phil. Mag. [5] xxxix. p. 309. 



\ See e.g. J. von Geitler, pp. 7-8, ' Inaugural Dissertation/ Bonn, 

 1893; E. H. Barton, pp. 70-71, Proc. Roy. Soc. vol. lvii. 1894; G. U. 

 Yule, Proc. Phys. Soc. t. c. pp. 384-387 ; Phil. Mag. t. c. pp. 334-337. 



$ 'Electrical Papers,' vol. ii. pp. 127 and 132-133. 



