PROFESSOR K. PEARSON AND MISS A. LEE ON THK VIISKATIONS 



The curve giving the velocity of this wave is found to be even more complex th;m 

 that for either the wave of transverse or of axial component electric force alone 

 (p. 177). In the neighbourhood of the origin the wave starts with infinite positive 

 velocity ; this falls to a finite but very great positive velocity at about y , and then 

 rises again and Incomes infinite at about ^ >. Beyond this we have a region of 

 negative velocity, starting with an infinite negative velocity, and falling to a velocity 

 even less than that of light at about '8556 2 . Then the velocity increases again, 

 becoming infinite at about v/2 2 , after which it takes an infinite positive value and 

 falls rapidly till it becomes equal to the velocity of light. Thus there are two centres, 

 one at about o, and another at about v/2 from the oscillator (inore exact values 

 are given below), from or towards which the waves appear to move with varying 

 velocities. In most cases the ^ <, centre would be far too near the oscillator for 

 experiment, but the ^/2^ centre, and even the point of negative velocity less than 

 that of light, appear to be well within the field of experiment, and actually within 

 the area inside which HERTZ made a good many experiments. Considering the 

 complex character of the velocity of this wave of electrical disturbance in the 

 equatorial plane, we feel doubtful as to what interpretation can possibly be put on 

 HERTZ'S interference experiments in this plane, especially on those made at a 

 moderate distance from the oscillator. 



The following figure gives the velocity curve of the equatorial electric wave 

 diagrammatically. The approximate values of the chief quantities concerned have 

 been calculated in the same manner as those on pp. 173-176, but it does not seem 

 necessary to reproduce the calculations. 





12TJ-.0 



t - cos X Seas* X-3 sin*X . 



Ob - sinxcosx d+\ sin* X) 



ah - i * cosec'x 



Oc - -BM6 t + -0393 



Od = SZ e </+ 1-2071 tenx> 



Cf - I-I-866O C \ t ^' 



- - -666o,neglecting 



