Size of Reflector in u Hertz s Experiment" 81 



We can now detect these waves in a variety of ways. 

 Hertz employed in his interference experiments a simple 

 circle of wire interrupted at one place by a short gap, the 

 wire being of such a length that the period of electric oscil- 

 lations from end to end on it is the same as that of the radia- 

 tion with which it is to be used, so that the currents induced 

 in the wire by a series of waves are synchronously reinforced 

 until the ends, always oppositely charged 3 overflow, and a 

 spark occurs. 



By means of perpendicular reflexion from a metallic sheet 

 a beam of the same period travelling in the opposite direction 

 is obtained which will interfere with the direct one, and a 

 series of loops and nodes result, just as in an organ-pipe. 

 The position of these nodes Hertz detected by the use of the 

 resonating receiver, the nodes and loops being distinguished 

 by the variation in the intensity of the sparking across the 

 gap as the distance of the resonator from the reflector was 

 changed. The magnetic and electric forces in these stationary 

 waves are everywhere complementary, that is, where one is 

 a maximum the other is a minimum. The first magnetic 

 node or place of minimum intensity of that force is situated 

 at one quarter the wave-length from the reflecting sheet, 

 and so on for the others, in the usual sequence of loops and 

 nodes. 



Some time since I observed that the distance of the nodes 

 from the reflector was influenced by its size, and a short 

 account was given in a paper in ' Nature/ vol. xl. p. 399, but 

 until the present no determinations were described systema- 

 tically made with various sized reflectors. 



When a number of square sheets of various sizes were tried 

 as reflectors, it was found that as the sheet became smaller 

 the distance of the node from the sheet became greater. 

 The increase seemed to tend towards becoming one eighth of 

 the wave-length as the size of the reflector diminished, but 

 with small sheets the intensity of the reflexion is very slight, 

 and so it soon becomes impossible to make any satisfactory 

 determination. 



Perhaps the most noticeable thing in connexion with re- 

 flexion from sheets of limited size is the great difference in 

 the effect, where the sheet is rectangular in shape, according 

 as its long dimension is parallel to the direction of the mag- 

 netic or electric component of the incident wave. This un- 

 doubtedly is connected with the accumulation of charge on 

 its edges, according as they lie in the direction suitable for it 

 or not. A long narrow strip (say anywhere between one 

 quarter and one half the wave-length in width) held with its 



Phil Mag. S. 5. Vol. 32. No. 194. July 1891. G 



