Size of Reflector in "Hertz's Experiment." 



87 



If the amplitude of the reflected beam be taken simply as 

 T-— , instead of its square, a somewhat more natural assump- 

 tion, the value found for x is about 15*8 — which is a shifting 

 inwards considerable in deficit. It is thus evident that, apart 

 from other considerations, a rapid falling-off in the intensity 

 of the reflected disturbance is quite competent to effect an 

 appreciable inward displacement of the node. However, it 

 must be remembered that in cases like the present, where the 

 intensity of one component changes rapidly with the distance, 

 the minimum spar king-position must only be considered as a 

 kind o£ pseudonode, not a true phasial one. 



Taking a long shaped strip of zinc about 20 cm. wide, the 

 experiment alluded to above, one somewhat analogous to 

 Stokes's ' Experimentum Crucis/ is easily made. The posi- 

 tion of the node when the strip is stretched in the electric 

 direction, that is with its small dimension in the magnetic, 

 will be found to be distant about one quarter the wave- 

 length, much the same as with an infinite sheet : but on 

 rotating the strip through 90° into the magnetic direction 

 the node will be displaced outward, showing clearly the 

 dependency of the effect on the two directions. 



In Table II. are given the results of the experiments 

 from which the second curve was plotted. In the first column 

 are the dimensions of the reflector in the direction of the 

 magnetic component. The mean of the four determinations 

 with each sized reflector is given in the last column. 



Table II. 



4 



14| 



8 



15* 



12 



16| 



20 



m 



24 



17 



28 



m 



32 



18 



36 ...... 



16f 



48 



16| 



Large 1 

 sheet j 



16* 



16* 



17 



m 



18 

 17* 

 17 

 17* 



17 



m 



16* 



17* 



17* 

 17* 



17 

 171 



17* 



14* 



14:6 



15* 



15-3 



16* 



16-4 



16* 



17 



17* 



172 



17* 



17-6 



171 



17-5 



17* 



17-1 



171 



17 



16| 



16-9 



It will be seen that it was possible to obtain determinations 

 with much narrower reflectors in the present experiments 

 than was previously found possible when dealing with the 

 strips held so as to be short in the electric direction. Thus a 

 given sized strip evidently must reflect less strongly when 

 held so that its longest edge is the one which becomes charged 



