Electric Waves along Wires by a Terminal Bridge. 45 



As a further test of the non-reflexion of waves by the 

 bridge G, the electrometer was afterwards used differentially, 

 the upper and lower needles having their disks attached to 

 points on the line a quarter-wave-length apart. The bridges 

 were placed at the end of the line 0*25 m. beyond the second 

 needle. With a no-resistance bridge the throws were positive 

 and of the order 50 scale-divisions ; with a simple discon- 

 nexion (" infinity bridge ") the throws were of the same order 

 but negative. The bridges F and H gave smaller throws, 

 positive and negative respectively, The bridge G also appeared 

 to yield a small throw ; but this was no larger than might be 

 due to a creep of the zero or an imperfection in the adjust- 

 ment of the electrometer-needles. The use of the differential 

 electrometer is thus seen to confirm the results of the expe- 

 riments conducted with a single needle. 



It should be noted that this paper deals only with the 

 absorption of waves by terminal bridges ; no intermediate 

 resistance-bridge will absorb all the waves arriving there. 

 The reflexion and transmission coefficients p r and t^ for an 

 intermediate bridge of resistance E, are given by * 



p'^mrh, anir, = mTL-v' • • • ( 9 > 



the notation being the same as that previously used. Thus 

 the condition for non-reflexion is B=g© , in which case all is 

 transmitted. Hence complete absorption is impossible. 



If, therefore, we wish to pass electric waves along wires 

 through any layer of dielectric, or through any other arrange- 

 ment which affects them, and are desirous of avoiding the 

 annoying disturbance due to return of the transmitted portion 

 after reflexion at the end of the line, the following method 

 will suffice. 



1. Place at the end of the line a bridge of the form herein 

 described, whose resistance has the value given by the theory 

 for plane waves. 



2. Test experimentally the absorbing-power of the bridge, 

 and, if necessary, adjust its resistance until no reflexion can 

 be detected. 



University College, Nottingham, 

 September 1896. 



* Oliver Heaviside'a ' Electrical Papers/ vol. ii. pp. 141-142. 



