Size of Reflector in "Hertz's Experiment" 83 



dealt with, and so, in speaking of the nodes, the places of 

 minimum magnetic force alone are meant. 



Care was taken, when determining the wave-length, to 

 have as reflector a sheet sufficiently large so that no increase 

 in size could produce any change in the distance of the nodes 

 from it. When this is the case, it may be considered infinite 

 in extent. The large sheet was then replaced in turn by 

 smaller sheets, and the position of the node in each case 

 observed. The experiments, as mentioned before, divide 

 themselves into two parts. First, where an infinite reflector 

 is, so to speak, gradually shortened in the direction of the 

 electric component of the wave, but remains unaltered at 

 right angles, whilst the accompanying change, if any, in the 

 position of the node is observed ; and, second, when the 

 shortening takes place in the direction of the magnetic com- 

 ponent. 



The general results of the first set of experiments are seen 

 at a glance by means of fig. 1. The abscissae here represent 

 the length of the reflector in the direction of the electric 

 component, while the ordinates represent on the same scale 

 corresponding to each sized reflector the distance of the re- 

 sonator from the reflector when placed in the first position of 

 minimum sparking. The length of the reflector in the direc- 

 tion of the magnetic component was 90 cm., as that was found 

 to be amply sufficient, i. e. increase was found to produce no 

 effect. The resonator was held in front of the centre of the 

 reflector. 



Fig. 1. 



1 ° 

































































































WIDT 



REFLECT 



i or 



INC STRIP 



It will be seen from the curve that when the reflector is 

 less than a wave-length the node begins to be shifted sensibly 

 outwards from the true quarter wave-length position, so that 

 to avoid these diffraction-effects mirrors should be at least a 

 wave-length in the electric direction. 



G2 



