648 



Jjr. C. V. Burton on the 



12. In fig. 2 let the plane of the paper be parallel to yz, 

 and let A, B, C, D be four planes parallel to xy. At a 

 definite instant, say £ = 0, let the first wave-train be entirely 

 confined to the region between C and D, and, moreover, 

 between the limits A and B, and at the same instant let 6 X 

 have the constant value b , P x having therefore simultaneously, 



Fio-. 2. 



between A and B, the constant value Yb . Similarly at time 



the reoior 



t = let the second wave-train be confined to 



between C and D, while between A and B, b 2 has the constant 



value b 



Thus the superposition of these two wave-trains gives rise, 



and P 2 consequently the constant value —Yb . 

 ition of these two wave-t 

 at time £ = 0, to uniform magnetic induction 



(a, b, c) = (0, 2b , 0) between A and B\ 

 while = P = Q = R between the same limits J ^ 



At the same time there is neither magnetic induction nor 

 electric force to the left of C or to the right of _D. 



13. Consider first the region to the left of C, where the 

 sether is at rest, and is free from magnetic induction and 

 electric force. Somewhere in this region let there be a 

 material system, and to fix ideas let this take the form of a 

 metal ring (I) which is rotating about an axis in its own 

 plane. The rotation in this case can cause no selective 

 circulation of positive and negative electrons around the 

 ring, such as would constitute an electric current. 



14. Next consider the region between A and B, where the 

 sether (as w r e provisionally assume) is drifting in the direction 

 of ^-increasing w r ith velocity &o/\/^7^ Du ^ i s otherwise in a 

 condition identical with that of the sether to the left of C. 



