HERT7/S RESEARCHES ON ELECTRICAL WAVES. 



151 



The reason that the discharges of a powerful iiulnction coil gives rise 

 to oscillatory inotioii is that firstly, it charges the terminals G and 6" 

 to a high potential ; secondly, it produces a sndden spark in the inter- 

 vening circuit ; and thirdly, as soon as the discharge begins the resist- 

 ance of the air space is so much reduced as to allow of oscillatory motion 

 being set up. If the terminal conductors are of very large capacity, for 

 example, if the terminals are in connection with a battery, the current 

 of discharge may indetinitely reduce the resistance of the air space, but 

 when the terminal conductors are of small capacity this must be done 

 by a separate discharge, and therefore under the conditions of the 

 author's experiments, an induction coil was absolutely essential for the 

 production of the oscillations. 



As the induced sparks in the experiment last described were several 

 millimeters in length, the author modified it by using the arrangement 

 shown in Fig. 4, and greatly increasing the distance between the micro- 

 meter circuit and the secondary circuit of the induction coil. The ter- 

 minal conductors G and C were 3 meters apart, and the wire between 

 them was of copper, 2 millimeters in diameter, with the discharger B 

 at its center. * 



x-f 



K c y>- 



■"Kzniy 



Fic. 4. 



The micrometer circuit consisted, as in the preceding experiments, of 

 a rectangle 80 centimeters broad by 120 centimeters long. With the 

 nearest side of the micrometer circuit at a distance of half a millimeter 

 from G Ti G' sparks 2 millimeters in length were obtained at M, and, 

 though the length of the sparks decreased rapidly as the distance of 

 the micrometer circuit was increased, a continuous stream of sparks was 

 still obtained at a distance of li meters. The intervention of the ob- 

 server's body between the micrometer circuit and t\w wire G B G' pro- 

 duced no visible effect on the stream of sparks at M. That the effect 

 was really due to the rectilinear condu(;tor G B G' was proved by the 

 fact that when one or other, or both, halves of this condu(;tor were re- 

 moved the sparks at M ceased. The s:iine effect was produced by draw- 



