82 Mr. F. T. Trouton on the Influence of 



length parallel to the magnetic direction, has the node nearly 

 as far out as if it were a square. But with the same strip 

 held at right angles, parallel to the electric direction, the node 

 is practically at one quarter the wave-length, just as it would 

 be for an infinite sheet. 



It was thought desirable, in making the experiments, to 

 use long strips for reflectors, as being a somewhat simpler 

 case than square plates. In the present determinations the 

 position of the node was found for a number of long strips of 

 regularly increasing widths, first, when the long dimension 

 of the reflector was held in the direction of the magnetic 

 component, in which case the great shifting outwards of the 

 node occurs ; and, secondly, when held at right angles, or in 

 the electric direction, in which case there is generally little 

 or no effect to be found. 



Nothing further as to the character of the effect than had 

 been previously observed was noticeable in the first case ; but 

 in the second case, that is where the length of the strip is 

 held in the electric direction, a distinct peculiarity was found 

 when the strip was very narrow. It may be remarked that 

 good reflexion can be obtained from strips in the second case 

 quite too narrow to afford reflexion when held at right angles 

 in the magnetic direction as in the first set. And it is with 

 these very narrow strips that the peculiarity is noticed. The 

 node, which until the strip is very narrow is practically un- 

 affected by the width of the strip, is now situated nearer the 

 reflector than one quarter the wave-length. This has con- 

 siderable interest attached to it because it was really observed 

 by Hertz in his original experiments, though he attributed it 

 accidentally to quite another cause. 



The vibrator or source of radiation employed in the follow- 

 ing experiments consisted of two brass cylinders with rounded 

 gilt ends (about 13 cm. long and 3 cm. in diameter), placed near 

 each other in the focal line of a cylindrical parabolic mirror 

 so as to give a parallel beam. It afforded radiation containing 

 waves of a variety of periods'*, but that selected by the " re- 

 sonator " employed had a wave-length of 68 cm. The reso- 

 nator, which was of the circular type, was placed in the centre 

 of the beam at about 2 m. from the vibrator, in front of the 

 metallic sheet used as reflector. It was always held so as to 

 receive the magnetic component only, that is in the plane 

 containing the axis of the vibrator, and with the diameter of 

 the circle through the spark-gap parallel to this axis ; in this 

 position, only the magnetic lines of force can take effect. 

 Thus throughout the following the magnetic force alone is 

 * ' Nature," vol. xli. p. 295. 



