of Electric Waves through Wires. 123 



bounding surface ; and we ought not to look for its existence 

 in the interior of the conductor*. 



To what has been said above about waves in wires we wish 

 to add just one remark concerning the method of carrying out 

 the experiments. If our waves have their seat in the neigh- 

 bourhood of the wire, the wave progressing along a single 

 isolated wire will not be propagated through the air alone ; 

 but since its effect extends to a great distance it will partly be 

 transmitted by the walls, the ground, &c, and will thus give 

 rise to a complicated phenomenon. But if we place opposite 

 each pole of our primary conductor in exactly the same way 

 two auxiliary plates, and attach a wire to each of them, 

 carrying the wires straight and parallel to each other to equal 

 distances, the effect of the waves makes itself felt only in the 

 region of space between the two wires. The wave progresses 

 solely in the space between the wires. We can thus take 

 precautions to propagate the effect through the air alone or 

 through another insulator, and the experiments will be more 

 convenient and free from error by this arrangement. For 

 the rest, the lengths of the waves are nearly the same in this 

 case as in isolated wires, so that with the latter the effect of 

 the disturbing causes is apparently not considerable. 



3. We can conclude from the above results that rapid 

 electric oscillations are quite unable to penetrate metallic 

 sheets of any thickness, and that it is, therefore, impossible 

 by any means to excite sparks by the aid of such oscillations 

 in the interior of closed metallic screens. If, then, we see 

 sparks produced by such oscillations in the interior of metallic 

 conductors, which are nearly, but not quite, closed, we shall 

 be obliged to conclude that the electric disturbance has forced 

 itself in through the existing openings. This view is also 

 correct, but it contradicts the usual theory in some cases so 

 completely that one is only induced by special experiments 

 to give up the old theory in favour of the new one. We shall 

 choose a prominent case of this kind, and by assuring our- 

 selves of the truth of our theory in this case, we shall demon- 

 strate its probability in all other cases. We again take 

 the arrangement which w r e have described in the previous 

 section and drawn in fig. 1 ; only we now leave the protect- 

 ing tube insulated from the central wire at 8. Let us now 

 send a series of waves through the apparatus in the direction 



* The calculation of the self-induction of such conductors on the 

 assumption of uniform density of current in their interior must therefore 

 lead to quite erroneous results. It is to be wondered at that the results 

 obtained with such wrong assumptions should still appear to approximately 

 coincide with truth. 



