Reception of Wireless Waves on Shielded Frame Aerial. 503 



difference in what direction the tube was pointed, provided 

 the frame itself was in the plane pointing to Paris. This 

 continued to be the case, even when the open ends of the 

 tube were closed by grids of copper wire connected at 

 numerous points to the spiral, the putting on or removal 

 of these grids making- no detectable difference in the 

 strength of the signals. 



Finally, the whole tube, including its ends, was completely 

 covered in with iron wire netting of about ^-incli mesh, in 

 contact with the copper spiral and end grids ; when it was 

 found that, though the signals were slightly further 

 diminished in intensity, say to about 20 per cent, of their 

 original strength, Paris could still be easily heard on the 

 frame, which continued to have directional properties quite 

 irrespective of the position of the wire-netting covered tube. 



It would appear from the experiments that while com- 

 pletely enclosing the frame in a conducting network 

 considerably damps the currents in the frame, and thus 

 diminishes the strength of the signals, such conducting net- 

 work by no means entirely screens the frame from incoming 

 w r aves of the 2600 metre length sent out on the spark 

 emissions of the Eiffel Tower. This result would appear to 

 be dependent on the considerable wave-length tested, as 

 copper-wire grids such as are mentioned above, with the 

 wires parallel to the plane of polarization of the waves, pretty 

 w r eil completely screen off the very short waves of a few 

 centimetres length, such as were used in the original lecture- 

 room experiments with Hertzian waves, as shown many 

 years ago by Sir Oliver Lodge. 



Further experiments were made with the frame placed 

 within a copper box in the form of a cube of two-feet dimen- 

 sions in each direction, made of sheet copper about 1/32 

 of an inch in thickness. This box was completely closed in 

 with soldered joints, excepting on one side, which was open, 

 but could be closed by means of a close-fitting lid also made 

 of similar sheet copper. In all the experiments the copper 

 box was connected to earth. The same circular frame aerial, 

 one foot in diameter, used in the previous trials, was em- 

 ployed, but a more 'compact, transformer-coupled G-valve 

 amplifier was used in place of the 5-valve resistance 

 amplifier and the separate 3-valve note magnifier. 



Preliminary experiments, in which only the frame aerial 

 was enclosed in the copper box — the amplifier, tuning con- 

 denser, telephone receiver, and batteries being outside — 

 having proved unreliable owing apparently to the outside 

 apparatus picking up the waves irrespective of the frame, 



