686 



Professor J. A. Fleming 



[May 24, 



renders the receiver more liable to disturbance by vagrant electric 

 waves due to atmospheric electricity, or other transmitters if of 

 sufficient strength. 



If, however, we employ a feebly damped radiator emitting long 

 trains of waves, say 20 to 50 waves, we can make use of a stiff er 

 receiver circuit, that is one containing a good deal of inductance, and 

 a detector such as Marconi's magnetic detector, which operates under 

 the action of feeble but oft-repeated and properly timed impulses. 

 We have then the advantage that the receiving circuit can be made 

 far less sensible to non-syntonic or isolated impulses unless these are 

 of extreme violence. 



Again, there are certain forms of detector — such as the thermal 

 and one of my own, to be described presently — which are affected by 



Fig. 7. 

 Antenna emitting Feebly Damped Telegraphic Electric Waves. 



the product of the mean-square value of the oscillations during a 

 train and by the number of trains per second. Hence, in this case 

 the effect on such a receiver at a given distance under the same con- 

 ditions will be increased by increasing the number of trains of oscilla- 

 tions per second, as well as by diminishing damping in each train. 

 It was tlierefore foreseen that we should gain some advanUige by the 

 use of undamped trains if some form of electric radiator could be 

 found emitting waves continuously, like the steady note of an organ- 

 pipe, rather than sounds like intermittent blasts on a trumpet or blows 

 on a drum. There are at least three ways in which these undamped 

 oscillations can be created. The first is a mechanical method, viz. 

 ])y aliigh-frecpiency alternator. Assuming we possess an alternating 

 current dynamo giving a current of a sufficiently high frequency, 

 we can connect one terminal to earth and the other to a radiating 



