358 SCIENCE PROGRESS 



umbrella ; it may otherwise be made of a collection of wires 

 which rise up vertically for a certain distance and then extend 

 horizontally for a still greater length. Whatever its form, when 

 the condenser discharges take place, rapidly reversed electric 

 currents are set up in this antenna, each explosion of the con- 

 denser discharge producing a train or collection of such electrical 

 vibrations in it. The antenna may be regarded as a kind of 

 electrical organ-pipe in which electrical oscillations are produced 

 in place of aerial oscillations ; these vibrations create electro- 

 magnetic waves in the aether and these waves are projected 

 in every direction with the velocity of light. 



In the condenser or dynamo circuit there is a key or inter- 

 rupter by which the trains of waves can be cut up into long 

 or short groups in accordance with the signals of the Morse 

 alphabet. The wireless transmitter is therefore a sort of light- 

 house sending out long and short flashes of electromagnetic 

 radiation which cannot affect the human eye but which do affect 

 the proper kind of sensitive receiver. 



Turning then to the receiver we find it also consists of three 

 parts, viz. (i) a receiving antenna which may or may not be the 

 same as the sending antenna; this captures or absorbs the 

 incident electromagnetic waves, very feeble oscillatory electric 

 currents being set up in it which are a copy on a very reduced 

 scale of those in the sending antenna, (ii) These antenna 

 oscillations are caused, in turn, to induce others in a nearly 

 closed circuit comprising a receiving condenser which is tuned 

 to the antenna; that is to say, it is arranged to have the same 

 natural period of electrical vibration. The energy picked up by 

 the receiving antenna is accumulated in this last circuit ; hence 

 electrical oscillations take place in this storing circuit which 

 are an exact imitation of those taking place in the distant 

 sending antenna and these are cut up into long and short 

 groups which are interpreted in accordance with the Morse 

 code. The third element in the receiver comprises the means 

 for making these signals visible or audible. At the present 

 time, the detectors in common use are the magnetic detector, the 

 glow-lamp or ionised gas detector and various forms of so-called 

 rectifying detector, the detector being associated with a tele- 

 phone. If a telephone receiver alone, of the ordinary magnetic 

 form, be connected across the terminals of the receiving con- 

 denser, no sound is produced in it unless the received electric 



