504 Mr. A. A. Campbell Swinton on the Reception of 



it was decided to put the whole of the apparatus and con- 

 nexions, as well as the frame, inside the box, and to listen to 

 the telephone receiver through a -J-inch rubber tube passed 

 into the box through a round hole in the latter. Consider- 

 able trouble was experienced in getting the apparatus to 

 work properly under these conditions, the close proximity 

 of the frame and the amplifier causing reactions that were 

 apt to lead to automatic howling, but with care clear signals 

 were again obtained. 



Experiments were again repeated with the 2600-metre 

 spark emission from the Eiffel Tower. 



Though putting the frame and other apparatus into the 

 box greatly reduced the strength of the received signals, 

 still, when the frame was pointed in the right direction, with 

 the open side of the copper box turned towards Paris, the 

 signals could be heard quite easily. They were probably 

 only about 5 per cent, of the strength obtained with the 

 frame completely unshielded. 



On closing up the open side of the box w T ith the copper 

 lid, it was found that as the lid was put on, the signals 

 further gradually diminished in strength. They were, how- 

 ever, still distinctly audible so long as the narrowest possible 

 slit or opening was left. Indeed, they only disappeared, and 

 did so quite suddenly, when the edges of the lid came into 

 actual contact with the box so as to form a closed continuous 

 electrical conductor round the frame. With the lid quite 

 closed, and making good electrical contact all round, no 

 trace of the signals could be heard. 



Experiments were also tried with a lid consisting of thin 

 tin-foil pasted on wood, in place of the copper lid. This lid 

 was just as effective as the copper one in stopping the signals. 

 When the tin-foil lid completely closed the aperture and made 

 good contact all round with the copper box, no trace of any 

 signals could be obtained. 



As mentioned, all these results were obtained with the 

 open side of the box facing Paris, but exactly similar results, 

 with no distinguishable difference as regards the strength 

 of the received signals, were obtained W'hen the box was 

 turned round so that its open side was pointing in the 

 exactly opposite direction from Paris. By such means it is 

 therefore not possible to ascertain the absolute direction of 

 the waves any better than with an unshielded frame. 



With the box turned so that its open side pointed in a 

 direction at right angles to the direction of Paris, either to 

 the right or to the left, but with the frame pointing in the 

 direction of Paris, no signals at all could be heard, though 



