378 Dr. Barton and Mr. Lownds on Reflexion and 



the interference effect produced by an intermediate resistance- 

 bridge placed on the line beyond the electrometer we have 

 simply to introduce its constants from equation (11) into 

 equation (43). This substitution gives 



d' "> 



<y =|=F-fG + H, 



where 



G= * 2 

 and 



\t^- u x r ' sin ' 2y 



H = ^- M {.Tr^+ ^ (sin ^-V sin ^27)) 



(45) 



2««-* 



= r— — 5-(l + n) COS (0 + 7T + J/). 



1 — /'l 



; 



For a no-resistance bridge this is further simplified by the 

 amplitude factor being unity. 



Experiments. 



55. Positions of Condensers. — For the transmitted system 

 the condensers were placed at FF' (fig. 1), the distance SF 

 being 59 metres + \/8. These tico distances were chosen to 

 eliminate any error which would arise if interference occurred 

 on the oscillator side of the condenser. This might con- 

 ceivably take place between the head of a wave-train arriving 

 at the condenser simultaneously with the departure of the tail 

 of a previous train reflected there. To reduce this anticipated 

 disturbance to a minimum, the distance SF was chosen of the 

 order 60 m. in preference to any smaller distance. It is 

 easily seen that if this interference was additive in one of the 

 positions chosen, then it would be subtractive in the other, 

 and both being small the arithmetic mean could be taken. 

 From the tables of readings it may be noted that neither of 

 these precautions was unnecessary. 



56. In the reflected system the distance ED of the con- 

 denser beyond the electrometer, denoted by l 2 in the theory, 

 was made 48 m. + X/8 ; the two positions being again adopted 

 to obviate any error due to interference. Here again the 

 precautions were not in vain. The wave-length X of the 



