Resistance of Compound Conductors. 497 



wire carrying the current to be observed. It is evident that 

 if the three alternating currents were of equal magnitude, 

 sounds of like loudness would be heard at equal distances 

 from the copper plate, whichever of the wires was touched ; 

 and, further, that the distances required to produce equal 

 sounds are inversely as the magnitudes of the corresponding 

 currents. 



A moment's observation proved that the currents in A and 

 B were about equal, and that in much greater. Numerical 

 estimates are best made with the aid of a second observer, who 

 does not see what contacts are being tried. My assistant 

 considered that about 6 \ inches of B and about 3-J inches of C 

 were required to give the same loudness as 6 inches of A. 

 This agrees with the approximate theory as well as could 

 be expected. 



If the single wire be reversed, then, according to theory 

 (resistances of German-silver wires neglected), the distribution 

 should be much the same as of steady currents under the sole 

 influence of resistance • that is, the currents in the branches 

 should be as + 2 to + 1, so that on the same scale the main 

 current would be +3. According to this the equivalent 

 lengths of the German-silver wires would be 6, 9, 18. The 

 numbers actually fouud by experiment were 6, 8, 17-J. 



In the first part of this experiment the current in one of 

 the branches is greater than in the main ; but I wished to 

 examine a case where both parts of the divided current 

 exceeded the whole. This could be done with a fivefold 

 coil, as described in the previous paper ; but such was not 

 ready to hand. In default thereof a common double coil, 

 belonging to a large electro-magnet, was enveloped with a 

 single layer of extra wire, which was combined in series with 

 one of the original wires. This arrangement is less favour- 

 able than one in which the two branches are in close juxta- 

 position throughout ; but I thought that with the aid of an 

 iron core it could be made to answer the purpose. Such a 

 core was provided in the form of a bundle of fine wires, 

 solid iron being obviously inappropriate. The two wires were 

 now connected in parallel and replaced the triple coil, the 

 arrangements in other respects remaining unchanged. 



The currents in the shorter branch (composed of one 

 original coil simply), in the longer branch (composed of the 

 other original and of the additional coil), and in the main 

 were now found to be inversely as the measured distances 

 •9, 1*3, 2*3, no regard being paid to sign, viz. as 1*11, *77, 

 •43. These numbers cannot be quite correct as they stand, 

 for the third should be equal to the difference between the 



