122 
WIRELESS TELEGRAPHY. 
consequence to increase the space influenced by the radiation; (2), to 
impress a definite wave length upon the radiations so that the receiving 
apparatus provided with similar wings may respond more readily to 
the influence by the action known as resonance, analogous to the tun¬ 
ing previously mentioned. 
This resonance effect is not so essential to the action as was once 
thought, as the receiver is not very discriminating as regards the 
exact wave length to which it will respond, but at extreme distances 
it may be important to tune the receiver to the transmitter. For 
sending over long distances those wings are done away with. (See 
Plate III.) 
(The third slide was thrown upon the screen.) 
In place of the wings one side of both receiving and transmitting 
apparatus is connected to a vertical wire; the other side to earth. 
The height of the vertical wire necessary depends on the distance sig¬ 
nals are to be sent. A height of 100 feet at each station has been 
found sufficient for transmitting about 3 miles (using an induction coil, 
giving about a 6 inch spark). With a vertical height of 200 feet sig¬ 
nals were sent a distance of over 8 miles. The diagram (Plate III.) 
shews how a kite was employed to raise the vertical wire. There is no 
reason why the arrangement should not be simplified by using an 
aluminium wire as the kite-string, the kite-string would then form the 
“ oscillating line.” It is found sometimes that it is unnecessary to 
“ earth ” the receiver. The transmitter should, however, be well. 
“ earthed” when using the vertical wire. 
Some of you may have noticed in the Entrance Hall, as you entered 
a piece of apparatus which was lent me by Captain Kennedy, R.E. 
It is the Marconi receiving apparatus, but there are certain little me¬ 
chanical details which do Captain Kennedy a good deal of credit on 
account of the ingenuity with which they are worked out. I propose 
to put this apparatus to a very practical test by sending a message to 
it from the transmitting apparatus on the table. I shall first attach 
this vertical wire (about ten feet long) to one side of the apparatus, 
and connect the other side to earth. The receiving apparatus outside 
has a similar vertical wire, but the earth wire is omitted. The receiv¬ 
ing instrument has also connected to it, iu "parallel” with the tapper, 
a “ Morse Recorder,” an instrument which registers the message sent 
in dots and dashes upon a running tape. I should be glad if someone 
would accompany the Quarter-master-Sergeant outside to see if the in¬ 
strument is working, and bring in the message recorded. 
(Experiment shewn :—One of the audience went to the receiving 
instrument outside. A few letters were sent on the Morse code from 
the transmitting apparatus. The tape with the message recorded was 
brought back, and handed round for inspection). 
You see that a moderate thickness of brickwork and doors will not 
prevent the passage of these electrical waves. The message, as you 
observed, was sent very slowly, but you must remember this apparatus 
is in its infancy, and infants must learn to walk before they can run. 
The principal portion of the receiving apparatus is the coherer. 
