302 Dr. E. H. Barton on the Attenuation of Electric 



wire, p = 2ir times the frequency of the waves, and //, is the 

 magnetic permeability of the wires. 



In the experiments under discussion the numerical data 

 were as follows : — ■ 



R=l*lxl0 5 C.GS. units per centim. (ascertained by 



P.O. Box tests, 10 metres of wire being 0*11 ohm). 

 p =2tt x 35 x 10 6 per second (deduced from A, and v). 

 ix =1 for copper wire. (In the intense field between the 

 poles of an electromagnet the wire in question was 

 found to be distinctly paramagnetic, but so was a roll 

 of paper; thus \x is taken as unity.) 

 These values put in (3) yield 



R'/R = 31-6 (4) 



Hence R for 1 centim. of the line, i. e. for 2 centim. of wire, 

 is 2*2 x 10 5 ; and we obtain 



R' per centim. of line = 69*5 x 10 5 . . . (5) 



Now for the line in question hv has been determined *, 

 both theoretically and experimentally, to be 56 X 10 10 C.G.S. 

 units. 



Thus we have for the theoretical value of the attenuation 

 constant 



o-=R'/2L0 = O-OOOOO62, (6) 



which is only half that determined experimentally. 



In the endeavour to account for this discrepancy two lines 

 of thought are open to us. 



(1) We may examine the order of accuracy of the expe- 

 riments and inquire in which direction the determination 

 probably errs; and (2) the applicability to the case in point 

 of the theoretical expression given may be discussed, and the 

 sense of the modification which it requires for rigorous appli- 

 cation to the present case may perhaps be inferred. These 

 will be taken in the above order. 



The experimental value is calculated upon the supposition 

 that the absorbing bridge used at the end of the line absorbs 

 all the electric waves incident upon it, and that the reflecting 

 bridge reflects all. If either supposition is incorrect the 

 phenomena are changed, and the value found for the attenuation 

 is in consequence affected. 



Now it was previously found that the absorbing bridge for 

 the line now in use must have a resistance of 560 ohms *. In 

 the present work it was accordingly endeavoured to keep the 



* " Absorption of Electric Waves," Phil. Mag. Jan. 1897 ; Proc. Phys. 

 Soc, Feb. and Mar. 1897. 



