160 hertz's researches on electrical waves. 



tion was insufficient, and it became necessary to consider the value both 

 of the E. M. F. induction and of the electro-static E. M. F. due to the 

 charged extremeties of the exciting circuit at each point of the microm- 

 eter circuit. 



The investigations to which these considerations led are described by 

 Dr. Hertz in a paper " On the Action of a Rectilinear Electrical Oscil- 

 lation upon a Circuit in its Vicinity," published in Wiedemann's Annalen, 

 1888, vol. XXXIV, page 155. 



In what follows, the exciting circuit will be spoken of as the primary, 

 and the micrometer circuit as the secondary. Hertz points out that the 

 reason that the electro-static efiect can not be neglected is to be found 

 in the extreme rapidity with which the elect ro-static forces change their 

 sign. If the electro- static alternations in the primary were compara- 

 tively slow they might attain a very high intensity without giving rise 

 to a spark in the secondary, since the electro-static distribution on tbe 

 secondary would vary so as to remain in equilibrium with the external 

 E. M. F. This however is impossible, because the variations in direc- 

 tion follow each other too rapidly for the distribution to follow them. 



In the present investigations the primary circuit consisted of a straight 

 copper wire 5 millimeters in diameter, carrying at its extremeties hollow 

 zinc spheres 30 centimeters in diameter. The centers of the spheres 

 were 1 meter apart, and at the middle of the wire was an air space three- 

 fourths centimeter in length. The wire was placed in a horizontal posi- 

 tion, and the observations were all made at points near to the horizontal 

 plane through it, which however did not of course aftect their gen- 

 erality, as the same effects would necessarily be i)roduced in any plane 

 through the horizontal wire. The secondary circuit consisted of a circle 

 of 35 centimeters, radius, of copper wire 2 millimeters in diameter, the 

 circle being broken by an air space capable of variation by means of a 

 micrometer screw. 



The circular form was selected for the secondary circuit because 

 the former investigations had shown that the sparking distance was 

 not the same at all points of the secondary, even when the con- 

 ductor as a whole remained unchanged in position, and with a circular 

 circuit it was easier to bring the air space 1o any part than if any other 

 form had been used. To attain this object the circle was made movable 

 about an axis passing through its center perpendicular to its plane. 



The circuits of the dimensions stated were very nearly in unison, and 

 they were further adjusted by means of little strips of metal soldered to 

 the extremities, and varied in length until the maximum sparking dist- 

 ance was obtained. 



We shall follow Dr. Hertz in first considering the subject theoretic- 

 ally, and then examining how far the experimental results are in accord- 

 ance with the theoretical conclusions. It will be assumed that the e. 

 M. F. at every point is a simple harmonic function of the time, but that 

 it does not undergo reversal in direction, and it will further beassumed 



