188 hertz's researches on electrical waves. 



ill the vicinity of the wall was observed to be a maximum on the side 

 towards tlie wall, and a minimum at the opposite side, and as the circle 

 was turned from one position to the other there was found to be no 

 point at which the sparks disappeared. As the distance from the wall was 

 increased, the sparks on the remote side gradually became weaker, and 

 vanished at a distance of 1.08 meters from the wall. When the circle was 

 carried farther in the same direction, the sparks appeared again on the 

 side remote from the wall, but were always weaker than on the side next 

 to it; the sparking however no longer passed from a maximum to a min- 

 imum merely, but vanished during the rotation once in tlie upper and 

 once in the lower half of the circle. The two null points gradually re- 

 ceded from their original coincident positions, until at the point B 

 they occurred at the highest and lowest i:)oints of the circle. As the 

 circle wasmoved further in the same direction, the null points passed 

 over to the side next to the wall, and approached each other again, 

 until when the center was at a distance of 2.35 meters from the wall the 

 two null points were again coincident. B must be exactly half-way be- 

 tween this point and the similar point previously observed, which gives 

 1.72 meters as the distance of B from the wall, a result which agrees, 

 within a few centimeters with that obtained by direct observation. 

 Moving further in the direction of C, the sparking at different points of 

 the circle became more nearly equal, until at C it was exactly so. In 

 this position there was no null point, and as the distance was farther 

 increased the phenomena recurred in the same order as before. 



Dr. Hertz found that the position of C could be determined within a 

 few centimeters, the determinations of its distance from the wall var^'- 

 ing from 4.10 to 4.15 meters ; he gives its most probable value as 4.12 

 meters. The point B could not be observed with any exactness, the 

 direct determinations varying from C to 7.5 meters as its distance from 

 the wall. It conld however be determined indirectly, for the distance 

 between B and C being found to be 2.4 meters, taking this as the true 

 value, A must have been 0.68 meter behind the surface of the wall, and 

 0.52 meters in front of it. The half-wave length would be 4.8 meters, 

 and by an indirect method it was found to be 4.5 meters, so that the 

 two results agree fairly well. Taking the mean of these as the true 

 value, and the velocity of light as the velocity of propagation, gives as 

 the vibration period of the apparatus 1.55/ hundred-millionths of a sec- 

 ond, instead of 1.4/ hundred-millionths, which was the theoretically cal- 

 culated value. 



A second series of experiments were made with a smaller apparatus, 

 and though the measurements could not be made with as much exact- 

 ness as those already described, the i^esults showed clearly that the 

 position of the nodes depends only on the dimensions of the conductors 

 and not on the material of the wall. 



Dr. Hertz states that after some i)ractice he succeeded in obtaining 



