Size of Reflector in "Hertz's Experiment" 85 



always easy, by diminishing the sparking-gap, to obtain spark- 

 ing in the minimum position ; this is not possible when large 

 sheets are employed as reflectors. 



Without being able to calculate in the case of a given sized 

 reflector what the amount of the equivalent acceleration in 

 phase should be, it can be seen that there should be a difference 

 in phase between the current induced in the reflector and the 

 incident wave when the reflector is short in the electric direc- 

 tion. For the edges afford a capacity and become charged 

 each vibration, the charges opposing the inducing electro- 

 motive force, so that the effective electromotive force will 

 reach its zero value sooner than when there are no edges for 

 the accumulation of charge. 



The problem of finding the reflexion from a reflector of limited 

 size presents considerable difficulties. An approximation, how- 

 ever, has been obtained by the author* by taking advantage 

 of Hertz's solution in the case of his "vibrator/' The short 

 reflector is assumed equivalent to another vibrator, and Hertz's 

 equations of the wave are found for it, by making the total 

 magnetic force due to both primary and secondary vibrator 

 behind the sheet zero. This necessitates assuming that the 

 reflexion comes from the central part only. This condition 

 renders it very limited in its application ; nevertheless calcu- 

 lation made by it of the position of the node shows it dis- 

 placed at all events in the right direction, and to an extent 

 comparable with observation. This method leads naturally 

 to looking at the cause of the displacement, from the point of 

 view of an increased velocity of the wave in the neighbour- 

 hood of the reflector, for so it appears in Hertz's theory of 

 his " vibrator." 



Fig. 2. 



ac 









































































REFLECTI 



OF 

 NC STRIP 



In the second set of experiments the narrowing of the re- 

 flector is in the magnetic direction. It will be seen from the 

 curve, fig. 2, plotted from the results, that the large outward 



* Phil. Mag. March 1890. 



